The X.Org Foundation provides an open source implementation of the X Window System.
XFree86
XFree86
4.4.0
Maintainers
XFree86, is a freely redistributable open-source implementation of
the X Window System. XFree86 runs primarily on UNIX and UNIX-like
operating systems such as Linux, all of the BSD variants, Sun Solaris
x86, Mac OS X (via Darwin), as well as other platforms like OS/2 and Cygwin.