GNU 
GNU's not Unix 
GNU (pronounced "guh-NOO") is a Unix-like operating system that's upwardly compatible with Unix. In addition to being an OS, it is also a philosophical statement about software development. GNU's creator, Richard Stallman, stipulated that GNU would be free for anyone to use, copy, alter, develop, share, and distribute, but no one could restrict its distribution in any way. The GNU General Public License (GNU GPL) establishes this free distribution system, called copyleft. Stallman's GNU Project is managed by the nonprofit Free Software Foundation. The core, or kernel, of the popular Linux OS is the best-known program that falls under the GNU GPL.