GNU Project in the context of GNU Compiler Collection

Free software, libre software, libreware sometimes known as freedom-respecting software is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions. Free software is a matter of liberty, not price; all users are legally free to do what they want with their copies of free software (including profiting from them) regardless of how much is paid to obtain the program. Computer programs are deemed "free" if they give end-users (not just the developer) ultimate control over the software and, subsequently, over their devices.

The right to study and modify a computer program entails that the source code—the preferred format for making changes—be made available to users of that program. While this is often called "access to source code" or "public availability", the Free Software Foundation (FSF) recommends against thinking in those terms, because it might give the impression that users have an obligation (as opposed to a right) to give non-users a copy of the program.

The Free Software Foundation (FSF) is a 501(c)(3) non-profit organization founded by Richard Stallman on October 4, 1985. The organization supports the free software movement, with its preference for software being distributed under copyleft ("share alike") terms, such as with its own GNU General Public License. The FSF was incorporated in Boston where it is also based.

From its founding until the mid-1990s, FSF's funds were mostly used to employ software developers to write free software for the GNU Project and its employees and volunteers have mostly worked on legal and structural issues for the free software movement and the free software community. Consistent with its goals, the FSF aims to use only free software on its own computers.

The GNU General Public Licenses (GNU GPL or simply GPL) are a series of widely used free software licenses, or copyleft licenses, that guarantee end users the freedom to run, study, share, or modify the software. The GPL was the first copyleft license available for general use. It was originally written by Richard Stallman, the founder of the Free Software Foundation (FSF), for the GNU Project. The license grants the recipients of a computer program the rights of the Free Software Definition. The licenses in the GPL series are all copyleft licenses, which means that any derivative work must be distributed under the same or equivalent license terms. The GPL states more obligations on redistribution than the GNU Lesser General Public License and differs significantly from widely used permissive software licenses such as BSD, MIT, and Apache.

Historically, the GPL license family has been one of the most popular software licenses in the free and open-source software (FOSS) domain. Prominent free software programs licensed under the GPL include the Linux operating system kernel and the GNU Compiler Collection (GCC). David A. Wheeler argues that the copyleft provided by the GPL was crucial to the success of Linux-based systems, giving the contributing programmers some assurance that their work would benefit the world and remain free, rather than being potentially exploited by software companies who would not be required to contribute to the community.

Richard Matthew Stallman (/ˈstɔːlmən/ STAWL-mən; born March 16, 1953), also known by his initials, rms, is an American free software movement activist and programmer. He campaigns for software to be distributed in such a manner that its users have the freedom to use, study, distribute, and modify that software. Software which ensures these freedoms is termed free software. Stallman launched the GNU Project, founded the Free Software Foundation (FSF) in October 1985, developed the GNU Compiler Collection and GNU Emacs, and wrote all versions of the GNU General Public License.

Stallman launched the GNU Project in September 1983 to write a Unix-like computer operating system composed entirely of free software. With that he also launched the free software movement. He has been the GNU project's lead architect and organizer, and developed a number of pieces of widely used GNU software including among others, the GNU Compiler Collection, GNU Debugger, and GNU Emacs text editor.

The free software movement is a social movement with the goal of obtaining and guaranteeing certain freedoms for software users, namely the freedoms to run, study, modify, and share copies of software. Software which meets these requirements, The Four Essential Freedoms of Free Software, is termed free software.

Although drawing on traditions and philosophies among members of the 1970s hacker culture and academia, Richard Stallman formally founded the movement in 1983 by launching the GNU Project. Stallman later established the Free Software Foundation in 1985 to support the movement.

GNU (/ɡnuː/ GNOO) is an extensive collection of free software (387 packages as of June 2025), which can be used as an operating system or can be used in parts with other operating systems. The use of the completed GNU tools led to the family of operating systems popularly known as Linux. Most of GNU is licensed under the GNU Project's own General Public License (GPL).

GNU is also the project within which the free software concept originated. Richard Stallman, the founder of the project, views GNU as a "technical means to a social end". Relatedly, Lawrence Lessig states in his introduction to the second edition of Stallman's book Free Software, Free Society that in it Stallman has written about "the social aspects of software and how Free Software can create community and social justice".

Since the 1990s, there has been ongoing debate over whether operating systems that use the Linux kernel in combination with GNU software should be referred to as Linux or GNU/Linux.

Supporters of the term Linux argue that it is more widely used in the media and by the general public, and that it serves as a practical shorthand for systems that combine the Linux kernel with software from a variety of sources, including the GNU Project.

Bash (short for "Bourne Again SHell") is an interactive command interpreter and scripting language developed for Unix-like operating systems. Created in 1989 by Brian Fox for the GNU Project, it is designed as a completely free software alternative for the Bourne shell, sh, and other proprietary Unix shells, supported by the Free Software Foundation. Having gained widespread adoption, Bash is commonly used as the default login shell for numerous Linux distributions. It also supports the execution of commands from files, known as shell scripts, facilitating automation.

The Bash command syntax is a superset of the Bourne shell's syntax, from which all basic features of the Bash syntax were copied. As a result, Bash can execute the vast majority of Bourne shell scripts without modification. Some other ideas were borrowed from the C shell, its successor tcsh, and the Korn Shell. It is available on nearly all modern operating systems, making it a versatile tool in various computing environments.

The Free Software Definition is a policy document written by Richard Stallman and published by the Free Software Foundation (FSF). It defines free software as software that grants users the freedom to use, study, share, and modify the software. The term "free" is used in the sense of "free speech", not "free of charge".

The earliest known publication of the definition appeared in the February 1986 edition of the now-discontinued GNU's Bulletin published by the FSF. Since 1996, the official version of the document has been maintained in the philosophy section of the GNU Project website. As of March 2025, the definition had seen 27 major revisions since it was originally published online and it had been translated into 65 languages. The FSF also publishes a list of licenses that meet this definition.