GNU is a recursive acronym, and it stands for GNU's Not Unix. This, no doubt, is because of Richard Stallman's grounding in Lisp.
The GNU Project has created a great many software packages, including gcc, gdb, sed, glibc, make, awk, find, and a good deal more besides. These packages make up a major portion of every Linux distribution.
The development of the GNU operating system, the Hurd, continues.