URL = http://www.gnu.org/
"The GNU Project was launched in 1984 to develop the GNU operating system, a complete Unix-like operating system which is free software—software which respects your freedom.
Unix-like operating systems are built from a software collection of applications, libraries, and developer tools—plus a program to allocate resources and talk to the hardware, known as a kernel.
GNU is often used with a kernel called Linux, and here is a list of ready-to-install GNU/Linux distributions which are entirely free software. The Hurd, GNU's kernel, is actively developed, but is still some way from being ready for daily use.
The combination of GNU and Linux is the GNU/Linux operating system, now used by millions and sometimes incorrectly called simply “Linux”.
The name “GNU” is a recursive acronym for “GNU's Not Unix!”; it is pronounced g-noo, as one syllable with no vowel sound between the g and the n." (http://www.gnu.org/gnu/gnu.html)