|Linking from code with a different licence||Yes|
The Unlicense is a public domain equivalent license for software which provides a public domain waiver with a fall-back public-domain-like license, similar to the CC Zero for cultural works. It includes language used in earlier software projects and has a focus on an anti-copyright message.
The text of the Unlicense is as follows:
This is free and unencumbered software released into the public domain.
Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.
In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
For more information, please refer to <http://unlicense.org/>
The Free Software Foundation states that "Both public domain works and the lax license provided by the Unlicense are compatible with the GNU GPL." However, for dedicating software to the public domain it recommends CC0 over the Unlicense, stating that CC0 "is more thorough and mature than the Unlicense".
Google does not allow its employees to contribute to projects under public domain equivalent licenses like the Unlicense (and CC0), while allowing contributions to 0BSD licensed and US government PD projects.
Notable projects that use the Unlicense include youtube-dl, Second Reality, and the source code of the 1995 video game Gloom.
In a post published on January 1 (Public Domain Day), 2010, Arto Bendiken, the author of the Unlicense, outlined his reasons for preferring public domain software, namely: the nuisance of dealing with licensing terms (for instance license incompatibility), the threat inherent in copyright law, and the impracticability of copyright law.
On January 23, 2010, Bendiken followed-up on his initial post. In this post, he explained that the Unlicense is based on the copyright waiver of SQLite with the no-warranty statement from the MIT License. He then walked through the license, commenting on each part.
In a post published in December 2010, Bendiken further clarified what it means to "license" and "unlicense" software.
In December 2010, Mike Linksvayer, the vice president of Creative Commons at the time, wrote in an identi.ca conversation "I like the movement" in speaking of the Unlicense effort, considering it compatible with the goals of the CC Zero (CC0) license, released in 2009. On January 1, 2011, Bendiken reviewed the progress and adoption of the Unlicense, saying it was "difficult to give estimates of current Unlicense adoption" but there were "many hundreds of projects using the Unlicense".
In January 2012, when discussed on OSI's license-review mailing list, the Unlicense was brushed off as a crayon license. In particular, it was criticized for being possibly inconsistent and non-standard, and for making it difficult for some projects to accept Unlicensed code as third-party contributions; leaving too much room for interpretation; and possibly being incoherent in some legal systems. A request for legacy approval was filed in March 2020, which led to a formal approval in June 2020, with an acknowledgement of a "general agreement that the document is poorly drafted".
In 2015, GitHub reported that approximately 102,000 of their 5.1 million licensed projects (2% of licensed projects on GitHub.com) used the Unlicense.
Until 2022, the Fedora Project recommended CC0 over the Unlicense because the former is "a more comprehensive legal text". However, in July 2022, the CC0 license became unsupported and software to be released in the Fedora distribution must not be under CC0, due to CC0 not waiving patent rights.
There is general agreement that the document is poorly drafted. It is an attempt to dedicate a work to the public domain (which, taken alone, would not be approved as an open source license) but it also has wording commonly used for license grants. There was some discussion about the legal effectiveness of the document, in particular how it would operate in a jurisdiction where one cannot dedicate a work to the public domain. The lawyers who opined on the issue, both US and non-US, agreed that the document would most likely be interpreted as a license and that the license met the OSD. It is therefore recommended for approval.
Fedora recommends use of CC-0 over this license, because it is a more comprehensive legal text around this tricky issue. It is also noteworthy that some MIT variant licenses which contain the right to "sublicense" are closer to a true Public Domain declaration than the one in the "Unlicense" text.
anybody affixing a licensing statement to open-source software is guilty of either magical thinking or of having an intention to follow up on the implied threat
@bendiken surely there's a better name than copyfree, but I like the movement and look fwd to your roundup.
In case it's of interest, I'm engaged in an ongoing Identi.ca conversation with Mike Linksvayer, the vice president of Creative Commons […] In short, the folks at Creative Commons are aware of the Unlicense initiative, and apparently supportive of it.
1 MIT 44.69%, 2 Other 15.68%, 3 GPLv2 12.96%, 4 Apache 11.19%, 5 GPLv3 8.88%, 6 BSD 3-clause 4.53%, 7 Unlicense 1.87%, 8 BSD 2-clause 1.70%, 9 LGPLv3 1.30%, 10 AGPLv3 1.05% (30 million × 2% × 17% = 102k)