GNU is a Unix-like computer operating system developed by the GNU Project, ultimately aiming to be a “complete Unix-compatible software system” composed wholly of free software. Development of GNU was initiated by Richard Stallman in 1983 and was the original focus of the Free Software Foundation (FSF). The latest alpha release of the GNU system is GNU 0.401, released on 1 April 2011, featuring GNU Hurd as the system’s kernel. Other (non-GNU) kernels, most famously the Linux kernel, can also be used with GNU. The FSF maintains that Linux, when used with GNU tools and utilities, should be considered a variant of GNU, and promotes the term GNU/Linux for such systems, (leading to the GNU/Linux naming controversy).
GNU is a recursive acronym for “GNU’s Not Unix!”, chosen because GNU’s design is Unix-like, but differs from Unix by being free software and containing no Unix code. Programs released under the auspices of the GNU Project are called GNU packages or GNU programs. The system’s basic components include the GNU Compiler Collection (GCC), the GNU Binary Utilities (binutils), the bash shell, the GNU C library (glibc), and GNU Core Utilities (coreutils). GNU developers have contributed Linux ports of GNU applications and utilities, which are now also widely used on other operating systems such as BSD variants, Solaris and Mac OS X.
The GNU General Public License (GPL), the GNU Lesser General Public License (LGPL), and the GNU Free Documentation License (GFDL) were written for GNU and the GNU Affero General Public License was written as an extended version of GPL version 3 for programs run over a network, but the GNU Project’s licenses are also used by many unrelated projects. A minority of the software used by GNU, such as the X Window System, is licensed under permissive free software licenses.
Richard Stallman views GNU as a “technical means to a social end”.