GNU /ɡnuː/ is an extensive collection of computer software that can be used to build a Unix-like operating system. GNU is composed wholly of free software. 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. and was the original focus of the Free Software Foundation (FSF). However, non-GNU kernels, most famously the Linux kernel, can also be used with GNU software.