GNU – large cumbersome animal. Also the subject of the recursive acronym GNU is Not Unix, in other words a Unix-like operating system which runs on a Linux kernel but contains no Unix code and is entirely free.

GNU was initiated by ex-MIT Richard Stallman in 1983 and is embroiled in a long-running controversy as to whether Linux is really a variant of GNU and should therefore really be referred to as GNU/Linux.

No G would be complete without GIMP – the GNU Image Manipulation Program. GIMP is a powerful, feature-rich program that runs on GNU/Linux, Windows and Mac. Download free here.