Portal is a 2007 puzzle-platform game developed and published by Valve. It was released in a bundle, The Orange Box, for Windows, Xbox 360 and PlayStation 3, and has been since ported to other systems, including Mac OS X, Linux, and Android (via Nvidia Shield).
Portal consists primarily of a series of puzzles that must be solved by teleporting the player's character and simple objects using "the Aperture Science Handheld Portal Device", a device that can create inter-spatial portals between two flat planes. The player-character, Chell, is challenged and taunted by an artificial intelligence named GLaDOS (Genetic Lifeform and Disk Operating System) to complete each puzzle in the Aperture Science Enrichment Center using the portal gun with the promise of receiving cake when all the puzzles are completed. The game's unique physics allows kinetic energy to be retained through portals, requiring creative use of portals to maneuver through the test chambers. This gameplay element is based on a similar concept from the game Narbacular Drop; many of the team members from the DigiPen Institute of Technology who worked on Narbacular Drop were hired by Valve for the creation of Portal, making it a spiritual successor to the game.
Portal was acclaimed as one of the most original games of 2007, despite criticisms of its short duration and limited story. The game received praise for its originality, unique gameplay and dark story with a humorous series of dialogue. GLaDOS, voiced by Ellen McLain in the English-language version, received acclaim for her unique characterization, and the end credits song "Still Alive", written by Jonathan Coulton for the game, was praised for its original composition and humorous twist. Portal is often cited as one of the greatest video games ever made. Excluding Steam download sales, over four million copies of the game have been sold since its release, spawning official merchandise from Valve including plush Companion Cubes, as well as fan recreations of the cake and portal gun. A standalone version, titled Portal: Still Alive, was released on the Xbox Live Arcade service in October 2008, which added 14 puzzles to the gameplay. A sequel, Portal 2, released in 2011, expanded on the storyline, adding several new gameplay mechanics and a cooperative multiplayer mode.
In Portal, the player controls the protagonist, Chell, from a first-person perspective as she is challenged to navigate through a series of test chambers using the Aperture Science Handheld Portal Device, or portal gun, under the watchful supervision of the artificial intelligence GLaDOS. The portal gun can create two distinct portal ends, orange and blue. The portals create a visual and physical connection between two different locations in three-dimensional space. Neither end is specifically an entrance or exit; all objects that travel through one portal will exit through the other. An important aspect of the game's physics is momentum redirection and conservation. As moving objects pass through portals, they come through the exit portal at the same direction that the exit portal is facing and with the same speed with which they passed through the entrance portal. For example, a common maneuver is to place a portal some distance below the player on the floor, jump down through it, gaining speed in freefall, and emerge through the other portal on a wall, flying over a gap or another obstacle. This process of gaining speed and then redirecting that speed towards another area of a puzzle allows the player to launch objects or Chell over great distances, both vertically and horizontally, referred to as 'flinging' by Valve. As GLaDOS puts it, "In layman's terms: speedy thing goes in, speedy thing comes out." If portal ends are not on parallel planes, the character passing through is reoriented to be upright with respect to gravity after leaving a portal end.
Chell and all other objects in the game that can fit into the portal ends will pass through the portal. However, a portal shot cannot pass through an open portal; it will simply deactivate or create a new portal in an offset position. Creating a portal end instantly deactivates an existing portal end of the same color. Moving objects, glass, special wall surfaces, liquids, or areas that are too small will not be able to anchor portals. Chell is sometimes provided with cubes that she can pick up and use to climb on or to hold down large buttons that open doors or activate mechanisms. Particle fields, known as "Emancipation Grills", occasionally called "Fizzlers" in the developer commentary, exist at the end of all and within some test chambers; when passed through, they will deactivate any active portals and disintegrate any object carried through. These fields also block attempts to fire portals through them.
Although Chell is equipped with mechanized heel springs to prevent damage from falling, she can be killed by various other hazards in the test chambers, such as turret guns, bouncing balls of energy, and toxic liquid. She can also be killed by objects hitting her at high speeds, and by a series of crushers that appear in certain levels. Unlike most action games at the time, there is no health indicator; Chell dies if she is dealt a certain amount of damage in a short period, but returns to full health fairly quickly. Some obstacles, such as the energy balls and crushing pistons, deal fatal damage with a single blow.
GameSpot noted, in its initial review of Portal, that many solutions exist for completing each puzzle, and that the gameplay "gets even crazier, and the diagrams shown in the trailer showed some incredibly crazy things that you can attempt". Two additional modes are unlocked upon the completion of the game that challenge the player to work out alternative methods of solving each test chamber. Challenge maps are unlocked near the halfway point and Advanced Chambers are unlocked when the game is completed. In Challenge mode, levels are revisited with the added goal of completing the test chamber either with as little time, with the fewest portals, or with the fewest footsteps possible. In Advanced mode, certain levels are made more complex with the addition of more obstacles and hazards.
The game features two characters: the player-controlled silent protagonist named Chell, and GLaDOS (Genetic Lifeform and Disk Operating System), a computer artificial intelligence that monitors and directs the player. In the English-language version, GLaDOS is voiced by Ellen McLain, though her voice has been altered to sound more artificial. The only background information presented about Chell is given by GLaDOS; the credibility of these facts, such as Chell being adopted, an orphan, and having no friends, is questionable at best, as GLaDOS is a liar by her own admission. In the "Lab Rat" comic created by Valve to bridge the gap between Portal and Portal 2, Chell's records reveal she was ultimately rejected as a test subject for having "too much tenacity"—the main reason Doug Rattman, a former employee of Aperture Science, moved Chell to the top of the test queue.
Portal takes place in the Aperture Science Laboratories Computer-Aided Enrichment Center—Aperture Science for short—which is a research facility responsible for the creation of the portal gun. According to information presented in Portal 2, the location of the complex is in the Upper Peninsula of Michigan. Aperture Science exists in the same universe as the Half-Life series, although connections between the two franchises are limited to references.
Information about the company, developed by Valve for creating the setting of the game, is revealed during the game and via the real-world promotional website. According to the Aperture Science website, Cave Johnson founded the company in 1943 for the sole purpose of making shower curtains for the U.S. military. However, after becoming mentally unstable from "moon rock poisoning" in 1978, Johnson created a three-tier research and development plan to make his organization successful. The first two tiers, the Counter-Heimlich Maneuver (a maneuver designed to ensure choking) and the Take-A-Wish Foundation (a program to give the wishes of terminally ill children to adults in need of dreams), were commercial failures and led to an investigation of the company by the U.S. Senate. However, when the investigative committee heard of the success of the third tier—a person-sized, ad hoc quantum tunnel through physical space, with a possible application as a shower curtain—it recessed permanently and gave Aperture Science an open-ended contract to continue its research. The development of GLaDOS, an artificially intelligent research assistant and disk-operating system, began in 1986 in response to Black Mesa's work on similar portal technology. A presentation seen during gameplay reveals that GLaDOS was also included in a proposed bid for de-icing fuel lines, incorporated as a fully functional disk-operation system that is arguably alive, unlike Black Mesa's proposal, which inhibits ice, nothing more. Roughly thirteen years later, work on GLaDOS was completed and the untested AI was activated during the company's bring-your-daughter-to-work day in May 2000. Immediately after activation, the facility was flooded with deadly neurotoxin by the AI. Events of the first Half-Life game occur shortly after that, presumably leaving the facility forgotten by the outside world due to apocalyptic happenings. Wolpaw, in describing the ending of Portal 2, affirmed that the Combine invasion, chronologically taking place after Half-Life and before Half-Life 2, had occurred before Portal 2's events.
The areas of the Enrichment Center that Chell explores suggest that it is part of a massive research installation. At the time of events depicted in Portal, the facility seems to be long-deserted, although most of its equipment remains operational without human control. During its development, Half-Life 2: Episode Two featured a chapter set on Aperture Science's icebreaker ship Borealis, but this was abandoned and removed before release.
Portal's plot is revealed to the player via audio messages or "announcements" from GLaDOS and visual elements inside rooms found in later levels. According to The Final Hours of Portal 2, the year is established to be "somewhere in 2010"—twelve years after Aperture Science has been abandoned.
The game begins with Chell waking up from a stasis bed and hearing instructions and warnings from GLaDOS, an artificial intelligence, about upcoming tests. Chell enters into distinct chambers that introduce players to the game's mechanics, sequentially. GLaDOS's announcements serve as instructions to Chell and help the player progress through the game, but also develops the atmosphere and characterizes the AI as a person. Chell is promised cake as her reward if she completes all test chambers.
Chell proceeds through the empty Enrichment Center, with GLaDOS as her only interaction. As the player nears completion, GLaDOS's motives and behavior turn more sinister; although she is designed to appear encouraging, GLaDOS's actions and speech suggest insincerity and callous disregard for the safety and well-being of the test subjects. The test chambers become increasingly dangerous as Chell proceeds, tests including a live-fire course designed for military androids, as well as some chambers flooded with a hazardous liquid. In another chamber, GLaDOS notes the importance of the Weighted Companion Cube, a waist-high crate with a single large pink heart on each face, for helping Chell to complete the test. However, GLaDOS declares it must be euthanized in an "emergency intelligence incinerator" before Chell can continue. Some later chambers include automated turrets with childlike voices (also voiced by McLain) that fire at Chell, only to sympathize with her after being destroyed or disabled.
After Chell completes the final test chamber, GLaDOS maneuvers Chell into an incinerator in an attempt to kill her. Chell escapes with the portal gun and makes her way through the maintenance areas within the Enrichment Center. GLaDOS panics and insists that she was pretending to kill Chell as part of testing. GLaDOS then asks Chell to assume the "party escort submission position", lying face-first on the ground, so that a "party associate" can take her to her reward, but Chell continues her escape. In this section, GLaDOS communes with Chell as it becomes clear the AI had killed everyone else in the center. Chell makes her way through the maintenance areas and empty office spaces behind the chambers, sometimes following graffiti messages which point in the right direction. These backstage areas, which are in an extremely dilapidated state, stand in stark contrast to the pristine test chambers. The graffiti includes statements such as "the cake is a lie", and pastiches of Emily Dickinson's poem "The Chariot", Henry Wadsworth Longfellow's "The Reaper and the Flowers", and Emily Brontë's "No Coward Soul Is Mine", referring to and mourning the death of the Companion Cube.
GLaDOS attempts to dissuade Chell with threats of physical harm and misleading statements as Chell makes her way deeper into the maintenance areas. Chell reaches a large chamber where GLaDOS's hardware hangs overhead. GLaDOS continues to threaten Chell, but during the exchange, a sphere falls off GLaDOS and Chell drops it in an incinerator. GLaDOS reveals that Chell has just destroyed the morality core of her conscience, one of the multiple "personality cores" that Aperture Science employees installed after the AI flooded the enrichment center with neurotoxin gas. With it removed, she can access its emitters again. A six-minute countdown starts as Chell dislodges and incinerates more of GLaDOS' personality cores, while GLaDOS discourages her both verbally, with taunts and juvenile insults, and physically by firing rockets at her. After Chell destroys the last personality core, a malfunction tears the room apart and transports everything to the surface. Chell is then seen lying outside the facility's gates amid the remains of GLaDOS. Following the announcement of Portal 2, the ending was expanded in a later update. In this retroactive continuity, Chell is dragged away from the scene by an unseen entity speaking in a robotic voice, thanking her for assuming the "party escort submission position".
The final scene, after a long and speedy zoom through the bowels of the facility, shows a Black Forest cake, and the Weighted Companion Cube, surrounded by a mix of shelves containing dozens of apparently inactive personality cores. The cores begin to light up, before a robotic arm descends and extinguishes the candle on the cake, causing the room to black out. As the credits roll, GLaDOS delivers a concluding report: the song "Still Alive", which declares the experiment to be a huge success, as well as serving to indicate to the player that GLaDOS is still alive.
Portal is Valve's spiritual successor to the freeware game Narbacular Drop, the 2005 independent game released by students of the DigiPen Institute of Technology; the original Narbacular Drop team was subsequently hired by Valve. Valve became interested in Narbacular Drop after seeing the game at DigiPen's annual career fair; Robin Walker, one of Valve's developers, saw the game at the fair and later contacted the team providing them with advice and offering to show their game at Valve's offices. After their presentation, Valve's president Gabe Newell quickly offered the entire team jobs at Valve to develop the game further. Newell later commented that he was impressed with the DigiPen team as "they had actually carried the concept through", already having included the interaction between portals and physics, completing most of the work that Valve would have had to commit on their own. To test the effectiveness of the portal mechanic, the team made a prototype in an in-house 2D game engine that is used in DigiPen. Certain elements have been retained from Narbacular Drop, such as the system of identifying the two unique portal endpoints with the colors orange and blue. A key difference in the signature portal mechanic between the two games, however, is that Portal's portal gun cannot create a portal through an existing portal unlike in Narbacular Drop. The game's original setting, of a princess trying to escape a dungeon, was dropped in favor of the Aperture Science approach. Portal took approximately two years and four months to complete after the DigiPen team was brought into Valve, and no more than ten people were involved with its development. Portal writer Erik Wolpaw, who, along with fellow writer Chet Faliszek, was hired by Valve for the game, claimed that "Without the constraints, Portal would not be as good a game".
For the first year of development, the team focused mostly on the gameplay without any narrative structure. Playtesters found the game to be fun but asked about what these test chambers were leading towards. This prompted the team to come up with a narrative for Portal. The Portal team worked with Half-Life series writer Marc Laidlaw on fitting the game into the series' plot. This was done, in part, due to the limited art capabilities of the small team; instead of creating new assets for Portal, they decided to tie the game to an existing franchise—Half-Life—to allow them to reuse the Half-Life 2 art assets. Wolpaw and Faliszek were put to work on the dialogue for Portal. The concept of a computer AI guiding the player through experimental facilities to test the portal gun was arrived at early in the writing process. They drafted early lines for the yet-named "polite" AI with humorous situations, such as requesting the player's character to "assume the party escort submission position", and found this style of approach to be well-suited to the game they wanted to create, ultimately leading to the creation of the GLaDOS character. GLaDOS was central to the plot, as Wolpaw notes "We designed the game to have a very clear beginning, middle, and end, and we wanted GLaDOS to go through a personality shift at each of these points." Wolpaw further describes the idea of using cake as the reward came about as "at the beginning of the Portal development process, we sat down as a group to decide what philosopher or school of philosophy our game would be based on. That was followed by about 15 minutes of silence and then someone mentioned that a lot of people like cake." The cake element, along with additional messages given to the player in the behind-the-scenes areas, were written and drawn by Kim Swift.
The austere settings in the game came about because testers spent too much time trying to complete the puzzles using decorative but non-functional elements. As a result, the setting was minimized to make the usable aspects of the puzzle easier to spot, using the clinical feel of the setting in the film The Island as reference. While there were plans for a third area, an office space, to be included after the test chambers and the maintenance areas, the team ran out of time to include it. They also dropped the introduction of the Rat Man, a character who left the messages in the maintenance areas, to avoid creating too much narrative for the game, though the character was developed further in a tie-in comic "Lab Rat", that ties Portal and Portal 2's story together. According to project lead Kim Swift, the final battle with GLaDOS went through many iterations, including having the player chased by James Bond lasers, which was partially applied to the turrets, Portal Kombat where the player would have needed to redirect rockets while avoiding turret fire, and a chase sequence following a fleeing GLaDOS. Eventually, they found that playtesters enjoyed a rather simple puzzle with a countdown timer near the end; Swift noted, "Time pressure makes people think something is a lot more complicated than it really is", and Wolpaw admitted, "It was really cheap to make [the neurotoxin gas]" in order to simplify the dialogue during the battle.
Chell's face and body are modeled after Alésia Glidewell, an American freelance actress and voice-over artist, selected by Valve from a local modeling agency for her face and body structure. Ellen McLain provided the voice of the antagonist GLaDOS. Erik Wolpaw noted, "When we were still fishing around for the turret voice, Ellen did a sultry version. It didn't work for the turrets, but we liked it a lot, and so a slightly modified version of that became the model for GLaDOS's final incarnation."
The Weighted Companion Cube inspiration was from project lead Kim Swift with additional input from Wolpaw from reading some "declassified government interrogation thing" whereby "isolation leads subjects to begin to attach to inanimate objects"; Swift commented, "We had a long level called Box Marathon; we wanted players to bring this box with them from the beginning to the end. But people would forget about the box, so we added dialogue, applied the heart to the cube, and continued to up the ante until people became attached to the box. Later on, we added the incineration idea. The artistic expression grew from the gameplay." Wolpaw further noted that the need to incinerate the Weighted Companion Cube came as a result of the final boss battle design; they recognized they had not introduced the idea of incineration necessary to complete the boss battle, and by training the player to do it with the Weighted Companion Cube, found the narrative "way stronger" with its "death". Swift noted that any similarities to psychological situations in the Milgram experiment or 2001: A Space Odyssey are entirely coincidental.
The portal gun's full name, Aperture Science Handheld Portal Device, can be abbreviated as ASHPD, which resembles a shortening of the name Adrian Shephard, the protagonist of Half-Life: Opposing Force. Fans noticed this similarity before the game's release; as a result, the team placed a red herring in the game by having the letters of Adrian Shephard highlighted on keyboards found within the game. According to Kim Swift, the cake is a Black Forest cake that she thought looked the best at the nearby Regent Bakery and Café in Redmond, Washington, and, as an Easter egg within the game, its recipe is scattered among various screens showing lines of binary code. The Regent Bakery has stated that since the release of the game, its Black Forest cake has been one of its more popular items.
Most of the game's soundtrack is non-lyrical ambient music composed by Kelly Bailey and Mike Morasky, somewhat dark and mysterious to match the mood of the environments. The closing credits song, "Still Alive", was written by Jonathan Coulton and sung by Ellen McLain (a classically-trained operatic soprano) as the GLaDOS character. A brief instrumental version of "Still Alive" is played in an uptempo Latin style over radios in-game. Wolpaw notes that Coulton was invited to Valve a year before the release of Portal, though it was not yet clear where Coulton would contribute. "Once Kim [Swift] and I met with him, it quickly became apparent that he had the perfect sensibility to write a song for GLaDOS." The use of the song over the closing credits was based on a similar concept from the game God Hand, one of Wolpaw's favorite titles. The song was released as a free downloadable song for the music video game Rock Band on April 1, 2008. The soundtrack for Portal was released as a part of The Orange Box Original Soundtrack.
Portal's soundtrack was released as part of a four-disc retail release, Portal 2: Songs To Test By (Collector's Edition), on October 30, 2012, featuring music from both games. The game's soundtrack became available via Steam Music on September 24, 2014.
Portal was first released as part of The Orange Box for Windows and Xbox 360 on October 10, 2007, and for the PlayStation 3 on December 11, 2007. The Windows version of the game is also available for download separately through Valve's content delivery system, Steam, and was released as a standalone retail product on April 9, 2008. In addition to Portal, the Box also included Half-Life 2 and its two add-on episodes, as well as Team Fortress 2. Portal's inclusion within the Box was considered an experiment by Valve; having no idea of the success of Portal, the Box provided it a "safety net" via means of these other games. Portal was kept to a modest length in case the game did not go over well with players.
In January 2008, Valve released a special demo version titled Portal: The First Slice, free for any Steam user using Nvidia graphics hardware as part of a collaboration between the two companies. It also comes packaged with Half-Life 2: Deathmatch, Peggle Extreme, and Half-Life 2: Lost Coast. The demo includes test chambers 00 to 10 (eleven in total). Valve has since made the demo available to all Steam users.
Portal was the first Valve-developed game to be added to the OS X-compatible list of games available on the launch of the Steam client for Mac on May 12, 2010, supporting Steam Play, in which players that had bought the game either on a Macintosh or Windows computer could also play it on the alternate system. As part of the promotion, Portal was offered as a free title for any Steam user during the two weeks following the Mac client's launch. Within the first week of this offer, over 1.5 million copies of the game were downloaded through Steam. A similar promotion was held in September 2011, near the start of a traditional school year, encouraging the use of the game as an educational tool for science and mathematics. Valve wrote that they felt that Portal "makes physics, math, logic, spatial reasoning, probability, and problem-solving interesting, cool, and fun", a necessary feature to draw children into learning. This was tied to Digital Promise, a United States Department of Education initiative to help develop new digital tools for education, and which Valve is part of.
Portal: Still Alive was announced as an exclusive Xbox Live Arcade game at the 2008 E3 convention, and was released on October 22, 2008. It features the original game, 14 new challenges, and new achievements. The additional content was based on levels from the map pack Portal: The Flash Version created by We Create Stuff and contains no additional story-related levels. According to Valve spokesman Doug Lombardi, Microsoft had previously rejected Portal on the platform due to its large size. Portal: Still Alive was well received by reviewers. 1UP.com's Andrew Hayward stated that, with the easier access and lower cost than paying for The Orange Box, Portal is now "stronger than ever". IGN editor Cam Shea ranked it fifth on his top 10 list of Xbox Live Arcade games. He stated that it was debatable whether an owner of The Orange Box should purchase this, as its added levels do not add to the plot. However, he praised the quality of the new maps included in the game. The game ranked 7th in a later list of top Xbox Live Arcade titles compiled by IGN's staff in September 2010.
During 2014 GPU Technology Conference on March 25, 2014, Nvidia announced a port of Portal to the Nvidia Shield, their Android handheld; the port was released on May 12, 2014.
See also: Critical reception of The Orange Box
Portal received critical acclaim, often earning more praise than either Half-Life 2: Episode Two or Team Fortress 2, two titles also included in The Orange Box. It was praised for its unique gameplay and dark, deadpan humor. Eurogamer cited that "the way the game progresses from being a simple set of perfunctory tasks to a full-on part of the Half-Life story is absolute genius", while GameSpy noted, "What Portal lacks in length, it more than makes up for in exhilaration." The game was criticized for sparse environments, and both criticized and praised for its short length. Aggregate reviews for the standalone PC version of Portal gave the game a 90/100 through 28 reviews on Metacritic. In 2011, Valve stated that Portal had sold more than four million copies through the retail versions, including the standalone game and The Orange Box, and from the Xbox Live Arcade version.
The game generated a fan following for the Weighted Companion Cube—even though the cube itself does not talk or act in the game. Fans have created plush and papercraft versions of the cube and the various turrets, as well as PC case mods and models of the Portal cake and portal gun. Jeep Barnett, a programmer for Portal, noted that players have told Valve that they had found it more emotional to incinerate the Weighted Companion Cube than to harm one of the "Little Sisters" from BioShock. Both GLaDOS and the Weighted Companion Cube were nominated for the Best New Character Award on G4, with GLaDOS winning the award for "having lines that will be quoted by gamers for years to come." Ben Croshaw of Zero Punctuation praised the game as "absolutely sublime from start to finish ... I went in expecting a slew of interesting portal-based puzzles and that's exactly what I got, but what I wasn't expecting was some of the funniest pitch black humor I've ever heard in a game". He felt the short length was ideal as it did not outstay its welcome.
Writing for GameSetWatch in 2009, columnist Daniel Johnson pointed out similarities between Portal and Erving Goffman's essay on dramaturgy, The Presentation of Self in Everyday Life, which equates one's persona to the front and backstage areas of a theater. The game was also made part of the required course material among other classical and contemporary works, including Goffman's work, for a freshman course "devoted to engaging students with fundamental questions of humanity from multiple perspectives and fostering a sense of community" for Wabash College in 2010. Portal has also been cited as a strong example of instructional scaffolding that can be adapted for more academic learning situations, as the player, through careful design of levels by Valve, is first hand-held in solving simple puzzles with many hints at the correct solution, but this support is slowly removed as the player progresses in the game, and completely removed when the player reaches the second half of the game. Rock, Paper, Shotgun's Hamish Todd considered Portal as an exemplary means of game design by demonstrating a series of chambers after the player has obtained the portal gun that gently introduce the concept of flinging without any explicit instructions. Portal was exhibited at the Smithsonian Art Exhibition in America from February 14 through September 30, 2012. Portal won the "Action" section for the platform "Modern Windows".
Since its release Portal is still considered one of the best video games of all time, having been included on several cumulative "Top Games of All Time" lists through 2018.
Portal won several awards:
The popularity of the game and its characters led Valve to develop merchandise for Portal made available through its online Valve physical merchandise store. Some of the more popular items were the Weighted Companion Cube plush toys and fuzzy dice. When first released, both were sold out in under 24 hours. Other products available through the Valve store include T-shirts and Aperture Science coffee mugs and parking stickers, and merchandise relating to the phrase "the cake is a lie", which has become an internet meme. Wolpaw noted they did not expect certain elements of the game to be as popular as they were, while other elements they had expected to become fads were ignored, such as a giant hoop that rolls on-screen during the final scene of the game that the team had named Hoopy.
A modding community has developed around Portal, with users creating their own test chambers and other in-game modifications. The group "We Create Stuff" created an Adobe Flash version of Portal, titled Portal: The Flash Version, just before release of The Orange Box. This flash version was well received by the community and the group has since converted it to a map pack for the published game. Another mod, Portal: Prelude, is an unofficial prequel developed by an independent team of three that focuses on the pre-GLaDOS era of Aperture Science, and contains nineteen additional "crafty and challenging" test chambers. An ASCII version of Portal was created by Joe Larson. An unofficial port of Portal to the iPhone using the Unity game engine was created but only consisted of a single room from the game. Mari0 is a fan-made four-player coop mashup of the original Super Mario Bros. and Portal.
Swift stated that future Portal developments would depend on the community's reactions, saying, "We're still playing it by ear at this point, figuring out if we want to do multiplayer next, or Portal 2, or release map packs." Some rumors regarding a sequel arose due to casting calls for voice actors. On March 10, 2010, Portal 2 was officially announced for a release late in that year; the announcement was preceded by an alternate reality game based on unexpected patches made to Portal that contained cryptic messages in relation to Portal 2's announcement, including an update to the game, creating a different ending for the fate of Chell. The original game left her in a deserted parking lot after destroying GLaDOS, but the update involved Chell being dragged back into the facility by a "Party Escort Bot". Though Portal 2 was originally announced for a Q4 2010 release, the game was released on April 19, 2011.
In other Steam news, Portal: First Slice – the official demo for the title named Game of the Year by over 30 publications – is now available for free to all gamers via Steam.