What is GNU?

GNU is a Unix-like operating system created and funded by the Free Software Foundation. One of the goals of the Free Software Foundation was an operating system composed entirely of free software. Many pieces, such as shells, utilities, and compilers were created for this purpose. The GNU operating system has yet to be fully completed, due to slow development and debates about design goals. Most of the programs created for GNU have been ported to other kernels and operating systems, most notably Linux.

Note: This question refers to an operating system. For the animal, see 'What is a gnu?' in the Related questions section below.