The GPL was written by Richard Stallman in 1989 for use with programs released as part of the GNU project. The original GPL was based on a unification of similar licenses used for early versions of GNU Emacs, the GNU Debugger and the GNU Compiler Collection. These licenses contained similar provisions to the modern GPL, but were specific to each program, rendering them incompatible, despite being the same license.^[1] Stallman’s goal was to produce one license that could be used for any project, thus making it possible for many projects to share code.

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An important vote of confidence in the GPL came from Linus Torvalds’ adoption of the license for the Linux kernel in 1992 (switching from an earlier license that prohibited commercial distribution).

By some measures, the GPL has become the single most popular license for free and open source software. As of January 2006, the GPL accounted for nearly 66% of the 41,962 free software projects listed on Freshmeat,^[2] and as of January 2006, about 68% of the projects listed on SourceForge.net.^[3] Similarly, a 2001 survey of Red Hat Linux 7.1 found that 50% of the source code was licensed under the GPL^[4] and a 1997 survey of MetaLab, then the largest free-software archive, showed that the GPL accounted for about half of the licenses used. One survey of a large repository of open-source software reported that in July 1997, about half the software packages with explicit license terms used the GPL.^[5] Prominent free software programs licensed under the GPL include the Linux kernel and the GNU Compiler Collection (GCC). Some other free software programs are dual-licensed under multiple licenses, often with one of the licenses being the GPL.

Some observers believe that the strong copyleft provided by the GPL was crucial to the success of the GNU/Linux operating system, giving the programmers who contributed to it the confidence that their work would benefit the whole world and remain free, rather than being exploited by software companies that would not have to give anything back to the community. Others believe that GNU/Linux could have done equally well under a BSD-style license.

The second version of the license, version 2, was released in 1991. Over the following 15 years, some members of the FOSS (Free and Open Source Software) community came to believe that some software and hardware vendors were finding loopholes in the GPL, allowing GPL-licensed software to be exploited in ways that were contrary to the intentions of the programmers. These concerns included tivoization (the inclusion of GPL-licensed software in hardware that will refuse to run modified versions of it); the use of closed-source, modified versions of GPL software behind web interfaces; and patent deals between Microsoft and Linux and Unix distributors that may represent an attempt to use patents as a weapon against competition from the GNU/Linux system.

The GNU General Public License (GNU GPL or simply GPL) is a widely used free software license, originally written by Richard Stallman for the GNU project. It is the license used by the GNU/Linux operating system. The GPL is the most popular and well known example of the type of strong copyleft license that requires derived works to be available under the same copyleft. Under this philosophy, the GPL is said to grant the recipients of a computer program the rights of the free software definition and uses copyleft to ensure the freedoms are preserved, even when the work is changed or added to. This is in distinction to permissive free software licences, of which the BSD licenses are the standard examples.

1. GNU Miscfiles ? several data files including standard airport, country, and language codes
2. GNU Chess
3. GNU Go
4. GnowSys ? a kernel for semantic computing (a distributed agent oriented knowledge base.)
5. Gnucap ? the GNU Circuit Analysis Package
6. Gnu Panorama ? 3D Framework, ray tracing
7. Gnu Maverik ? Virtual Reality microkernel
8. 3DLDF ? graphics package

1. GNU Octave ? a program for numerical computations similar to MATLAB
2. GSL ? the GNU Scientific Library
3. GMP ? arbitrary precision numerical calculation programming library
4. GDL ? GNU data language, compatible with IDL

1. Gnash ? player and browser plugin for the Adobe Flash file format
2. GNU Alexandria ? package of the GNU system that makes use of GNU Bayonne to provide a means to deliver access to electronic content and services for the blind over the public telephone network from a GNU/Linux server
3. GNU Anubis ? outgoing mail processor that sits between the MUA (Mail User Agent) and the MTA (Mail Transport Agent)
4. GNU Aspell ? spell checker designed to eventually replace Ispell
5. GNU Accounting Utils ? set of utilities providing statistics on users and processes for GNU/Linux (last, ac, accton, lastcomm, sa, dump-utmp, dump-acct)
6. GNU Emacs ? the Emacs editor of the GNU operating system
7. GNU Parted ? Partitioning program
8. GNU Privacy Guard ? PGP encryption replacement
9. GNU wget ? advanced file retrieval from networks and the Internet
10. GNUnet ? decentralized, peer-to-peer communication network designed to be resistant to censorship
11. GNU Robots ? game for computer programmers
12. GnuTLS ? TLS replacement protocol
13. GNU Typist Universal (multi-lingual) typing tutor
14. Gnuzilla ? Internet suite

1. GIMP ? the GNU Image Manipulation Program is a bitmap image editor that rivals Photoshop
2. GTK+ ? the GIMP Toolkit, contains the GTK+, GDK, and GLib set of libraries (used by the GIMP and GNOME)
3. GNOME ? the GNU Network Object Model Environment, the official GNU Desktop
4. GNUstep ? implementation of the OpenStep libraries and development tools for graphical applications

1. GNU build system ? contains autoconf, autogen, and automake
2. Gnulib ? portability library designed for use with the GNU build system
3. GNU Binutils ? contains the GNU assembler (as) and the GNU linker (ld)
4. GNU make ? the Make program for GNU
5. GNU Compiler Collection ? optimizing compiler for many programming languages, including C, C++, Fortran, Ada, and Java.
6. GNU Debugger ? an advanced debugger (gdb)
7. GNU C Library (glibc) ? POSIX compliant C library for GNU/Hurd and GNU/Linux
8. GNU pth ? software threads for POSIX-compatible operating systems.
9. GNU libtool ? Shared library support
10. GNU m4 ? macro processor
11. GNU Gettext ? internationalization library
12. DotGNU ? replacement for Microsoft .NET
13. GNU Classpath ? libraries for Java
14. GNU bison ? parser generator intended to replace yacc
15. GNU Guile ? embeddable Scheme interpreter
16. BFD ? object file library
17. GNU MDK ? a development kit for programming in MIX
18. GNU indent ? a program to indent C and C++ source code.
19. GNU FriBidi ? a library that implements Unicode’s Bidirectional Algorithm
20. MIT/GNU Scheme ? interpreter, compiler and library for the Scheme programming language developed at the Massachusetts Institute of Technology.
21. SmartEiffel ? the GNU Eiffel compiler
22. GNU Smalltalk ? ANSI Smalltalk-98 implementation (interpreter and class library).
23. CLISP ? ANSI Common Lisp implementation (compiler, debugger, and interpreter)
24. GNU Common Lisp ? an implementation of Common Lisp

Prominent components of the GNU system include the GNU Compiler Collection (GCC), the GNU C Library (glibc), the GNU Emacs text editor, and the GNOME desktop environment.

Many GNU programs have been ported to a multitude of other operating systems, including various proprietary platforms such as Microsoft Windows and Mac OS X. They are often installed on proprietary UNIX systems as a replacement for proprietary utilities, however, this is often a hot topic among enthusiasts, as the motive for developing these programs was to replace those systems with free software, not to enhance them. These GNU programs have in contested cases been tested to show as being more reliable than their proprietary Unix counterparts.^[13]

A list of packages that are well known in the free software community includes:

• System software
  • Bison – parser generator intended to replace yacc
  • Bash – Unix shell
  • BFD – object file library
  • Classpath – libraries for Java
  • Coreutils – basic Unix utilities such as cat, ls, and rm
  • Emacs – extensible, self-documenting text editor
  • GNU C Library – Standard POSIX C library, plus additional functionality
  • gzip – a library and program for data compression
  • The GNU toolchain for software development:
    • GNU Binary Utilities – assembler, linker, and related tools
    • GNU build system – Autoconf, Automake, Libtool
    • GCC – optimizing compiler for many programming languages, including C, C++, Fortran, Ada, and Java
    • GDB – debugger
  • Screen – a terminal multiplexer
  • Texinfo – documentation system for producing online and printed manuals
  • Wget – advanced file retrieval from networks and the Internet
  • GNUnet – decentralized, peer-to-peer communication network designed to be resistant to censorship
  • GNU Hurd – a microkernel-based set of servers that perform the same function as a Unix kernel
• Application software
  • GIMP – GNU Image Manipulation Program
  • Gnash – player for movies in Adobe Flash format.
  • GMP – arbitrary precision numerical calculation programming library
  • GNOME – graphical desktop environment
  • GNU LilyPond – sheet music engraving program
  • GNU Octave – program for numerical computations similar to MATLAB
  • GNU Privacy Guard (GnuPG) – free encryption tool which can replace PGP
  • GNU Robots – small but addictive game for computer programmers
  • GNU Scientific Library – is a software library for numerical calculations in applied mathematics and science
  • GNUstep – implementation of the OpenStep standard for a set of libraries and development tools for graphical applications
  • GNU Guile – embeddable Scheme interpreter

As of 2007-02-17, there are a total of 319 GNU packages hosted on the official GNU development site

The GNU Project requires that contributors assign the copyright for GNU packages to the Free Software Foundation,^[9] although exceptions have been made in the case of MULE,^[10] and large parts of GNOME. Most GNU packages are licensed under the GPL, while a few use the LGPL, and an even smaller number use other free software licenses.

Owning the copyright for the software allows FSF to enforce the licenses and to make changes in the licenses.^[11]

Ordinarily, copyright law prohibits people from copying and distributing a work, but FSF wrote a license for the GNU software which grant recipients permission to copy and redistribute the software. For most of the 80s, each GNU package had its own license - the Emacs General Public License, the GCC General Public License, etc. In 1989, FSF published a single license they could use for all their software, and which could be used by non-GNU projects: the GNU General Public License (GPL).

This license is now used by most GNU programs, as well as a large number of free software programs that are not part of the GNU project; it is the most commonly used free software license. It gives all recipients of a program the right to run, copy, modify and distribute it, while forbidding them from imposing further restrictions on any copies they distribute. This idea is often referred to as copyleft.

In 1991, the GNU Lesser General Public License (LGPL) was written for certain libraries. 1991 also saw the release of version 2 of the GNU GPL. The GNU Free Documentation License (FDL), for documentation, followed in 2000.

Most GNU software is distributed under the GPL. A minority is distributed under the LGPL, and a handful of packages are distributed under permissive free software licences.

The initial plan for GNU was to be mostly Unix-compatible, while adding enhancements where they were useful. By 1990, the GNU system had an extensible text editor (Emacs), a very successful optimizing compiler (GCC), and most of the core libraries and utilities of a standard Unix distribution. As the goal was to make a whole free operating system exist - rather than necessarily to write a whole free operating system - Stallman tried to use existing free software when possible. In the 1980s there was not much free software, but there was the X Window System for graphical display, the TeX typesetting system, and the Mach micro kernel. These components were integrated into GNU.

The main component still missing was the kernel. In the GNU Manifesto, Stallman had mentioned that “an initial kernel exists but many more features are needed to emulate Unix.” He was referring to TRIX, a remote procedure call kernel developed at Massachusetts Institute of Technology, whose authors had decided to distribute it as free software, and was compatible with Version 7 Unix. In December 1986, work had started on modifying this kernel. However, the developers eventually decided it was unusable as a starting point, primarily because it only ran on “an obscure, expensive 68000 box” and would therefore have to be ported to other architectures before it could be used.

The GNU Project’s early plan was to adapt the BSD 4.4-Lite kernel for GNU. Thomas Bushnell, the initial Hurd architect said in hindsight that “It is now perfectly obvious to me that this would have succeeded splendidly and the world would be a very different place today”.^[5] However, due to a lack of cooperation from the Berkeley programmers, Richard Stallman by 1988, the Mach message-passing kernel being developed at Carnegie Mellon University was being considered instead, although its release as free software was delayed until 1990 while its developers worked to remove code copyrighted to AT&T.

The design of the kernel was to be GNU’s largest departure from “traditional” Unix. GNU’s kernel was to be a multi-server microkernel, and was to consist of a set of programs called servers that offers the same functionality as the traditional Unix kernel. Since the Mach microkernel, by design, provided just the low-level kernel functionality, the GNU Project had to develop the higher-level parts of the kernel, as a collection of user programs. Initially, this collection was to be called Alix, but developer Thomas Bushnell later preferred the name Hurd, so the Alix name was moved to a subsystem and eventually dropped completely.^[6] Eventually, development progress of the Hurd became very slow due to ongoing technical issues.^[7]

Despite an optimistic announcement by Stallman in 2002^[8] predicting a release of GNU/Hurd, further development and design are still required. The latest release of the Hurd is version 0.2. It is fairly stable, suitable for use in non-critical applications. As of 2005, Hurd is in slow development, and is now the official kernel of the GNU system. There is also a project working on porting the GNU system to the kernels of FreeBSD, NetBSD, and OpenSolaris.

After the Linux kernel became usable, Linux became the most common host for GNU software. The GNU project coined the term GNU/Linux for such systems.

See also: GNU/Linux naming controversy