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).