GNU /ɡnuː/ is an operating systemand an extensive collection of computer software. GNU is composed wholly of free software, most of which is licensed under GNU's own GPL. 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.The GNU project includes an operating system kernel, GNU HURD, which was the original focus of the Free Software Foundation (FSF).However, non-GNU kernels, most famously Linux, can also be used with GNU software; and since the kernel is the least mature part of GNU, this is how it is usually used. The combination of GNU software and the Linux kernel is commonly known as Linux (or less frequently GNU/Linux; see GNU/Linux naming controversy). With the April 30, 2015 release of the Debian GNU/HURD 2015 distro, GNU OS now provides the components to assemble an operating system that users can install and use on a computer. This includes the GNU Hurd kernel, that is currently in a pre-production state. The Hurd status page states that "it may not be ready for production use, as there are still some bugs and missing features. However, it should be a good base for further development and non-critical application usage." Due to Hurd not being ready for production use, in practice these operating systems are Linux distributions. They contain the Linux kernel, GNU components and software from many other free software projects. Looking at all program code contained in the Ubuntu Linux distribution in 2011, GNU encompassed 8% and the Linux kernel 9%. Richard Stallman, the founder of the project, views GNU as a "technical means to a social end" or in other words is a technical avenue to pursue social justice. Relatedly Lawrence Lessig states in his introduction to the 2nd 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." Development of the GNU operating system was initiated by Richard Stallman at the Massachusetts Institute of Technology (MIT) Artificial Intelligence Laboratory as a project called the GNU Project which was publicly announced on September 27, 1983, on the net.unix-wizards and net.usoft newsgroups by Richard Stallman. Software development began on January 5, 1984, when Stallman quit his job at the Lab so that they could not claim ownership or interfere with distributing GNU components as free software. Richard Stallman chose the name by using various plays on words, including the song The Gnu. The goal was to bring a wholly free software operating system into existence. Stallman wanted computer users to be "free", as most were in the 1960s and 1970s – free to study the source code of the software they use, free to share the software with other people, free to modify the behavior of the software, and free to publish their modified versions of the software. This philosophy was later published as the GNU Manifesto in March 1985. Richard Stallman's experience with the Incompatible Timesharing System (ITS), an early operating system written in assembly language that became obsolete due to discontinuation of PDP-10, the computer architecture for which ITS was written, led to a decision that a portable system was necessary. It was thus decided that the development would be started using C and Lisp as system programming languages, and that GNU would be compatible with Unix. At the time, Unix was already a popular proprietary operating system. The design of Unix was modular, so it could be reimplemented piece by piece. Much of the needed software had to be written from scratch, but existing compatible third-party free software components were also used such as the TeX typesetting system, the X Window System, and the Mach microkernel that forms the basis of the GNU Mach core of GNU Hurd (the official kernel of GNU). With the exception of the aforementioned third-party components, most of GNU has been written by volunteers; some in their spare time, some paid by companies, educational institutions, and other non-profit organizations. In October 1985, Stallman set up the Free Software Foundation (FSF). In the late 1980s and 1990s, the FSF hired software developers to write the software needed for GNU. As GNU gained prominence, interested businesses began contributing to development or selling GNU software and technical support. The most prominent and successful of these was Cygnus Solutions, now part of Red Hat.