"Ever wonder why some people refer to Linux as GNU/Linux? The
official explanation is that Linux is merely an OS kernel that
relies on GNU software to make a complete operating system. GNU was
announced in 1983 as a future replacement operating system for
Unix, to be made up entirely of free software.
"But after more than 25 years in development, GNU remains
incomplete: Its kernel, Hurd, has never really made it out of the
starting blocks. (I'll refer to the complete OS as "GNU Hurd" to
avoid confusion with other GNU software.) Almost no one has
actually been able to use the OS; it's really more a set of ideas
than an operating system."