XFree86
XFree86 was a free open-source implementation of X11. In 2004 XFree86 changed to a more restrictive license for the 4.4 release, prompting the X.Org Foundation to fork the code just before the license change, which with some additional work was released as Xorg 6.7. Virtually all operating systems now use Xorg, and the XFree86 projct has been inactive since 2009.