.pkg (package) is a filename extension used for several file formats that contain packages of software and other files to be installed onto a certain device, operating system, or filesystem, such as the macOS, iOS, PlayStation Vita, PlayStation 3, and PlayStation 4.

• The macOS and iOS operating systems made by Apple use .pkg extensions for Apple software packages using the Xar format internally.
• PlayStation Vita, Sony PlayStation 3, Sony PlayStation 4 — used for installation of PlayStation Vita, PlayStation 3 and PlayStation 4 software, applications, homebrew, and DLC from the PlayStation Store^[1]
• Solaris,^[2] or SunOS operating system (OS) and illumos - Denotes software packages that can be installed, removed and tracked using the pkgadd, pkgrm, and pkginfo commands. Solaris is a derivative of the AT&T UNIX OS, and the .pkg extension was also used on AT&T UNIX System V OS.
• AT&T UNIX System V .pkg files are cpio archives that contain specific file tree structures.^[3]
• Symbian use .pkg files to store configuration information used to generate .sis installer packages.^[4]
• BeOS Used .pkg files in the 90's as part of their software package platform. Be Inc. bought Starcode Software Inc. and acquired their packaging tools.^{[citation needed]}
• Apple Newton operating system used files ending in .pkg for Newton applications and software. As a result, when seen from the Mac OS X Finder, Newton applications appear the same as Mac OS X Installer packages, however they do not share their file format.^{[citation needed]}
• PTC/CoCreate 3D Modeling application use .pkg files to store model files. This .pkg file uses the zip file format.^{[citation needed]}
• Microsoft is said to use .pkg files for profile storage on Xbox Live.^{[citation needed]}
• L3 Avionics systems use some .pkg files for software updates.^{[citation needed]}