X was originally developed by the Massachusetts Institute of Technology ("Athena Project") in the early to mid '80s. It has since become the standard graphic server on all commercially available UNIX variants. Around 1988, the MIT Group turned the project over to the MIT X Consortium, which took control of the development and distribution of X. Subsequently, in 1993, the members transferred all rights to X Window System to the X Consortium, Inc. And, once again, in 1996, all rights to the X Window System were placed with the Open Software Foundation as the X Consortium shut down. Before closing, however, the X Consortium brought us X11R6 (release 6.3, to be exact). Around that same time (1996), the Open Software Foundation merged with X/Open Company Ltd., creating the organization we know today as The Open Group. The Open Group changed the X Window System license to a fee for commercial distribution in 1998 with the release of X11R6.4. The change caused a shift as developers moved to an already prominent group that did not charge a fee. The group was known the XFree86 project.
Even though the X Window System got its start in 1984, a version for the PC did not come about until a German student ported a version to his 386-based PC. In the early '90s, Thomas Roell ported the X Window System, based on the X11R4, to his 386 PC and called it X386. In 1992, four developersDavid Dawes, Glenn Lai, Jim Tsillas, and David Wexelblatcame together to create a free, open source version of an X server for the PC UNIX-like systems. Initially, the project produced a version of the X server derived from Roell's X386. Of course, because the term X386 was already in use, the team came up with the new name, and in 1992, XFree86 was born.
To keep the XFree86 project current with the latest code of the day, the group had to join the X Consortium, which controlled the X Window System source. The group incorporated and joined the X Consortium, enabling XFree86 to be integrated with X11R6. This spurred new versions of the XFree86 product; however, the group did not stay on the same page for long. As mentioned previously, the X Consortium handed all rights to the X Window System over to The Open Group in 1996. However, when the group changed the license with the release of X11R6.4, The XFree86 Project, Inc. stopped referencing the new X11R6 code, which was under the new license. This circumvented the licensing issue for the XFree86 project. Now the XFree86 project was in full swing.
The Open Group did not expect such a backlash of events, so X11R6.4 was rereleased under a "new license." Essentially, the license was the same as the original, so the group created another entity to direct X development. A new spin-off organization that was created by The Open Group in 1999 is called X.org (http://www.X.org), which today's Linux users who are running a recent release of a distribution might recognize.
At that point, two main groups were developing the X Window System: X.org has the official rights to the code, and XFree86 is a free, open source implementation of X. Fast-forwarding a few years, the XFree86 group released several newer revisions of its product. In January 2004, the The Xfree86 Project, Inc. released version 4.4 under a new license. With this new license, which only made a few controversial changes, the X.org Foundation was on the receiving end of developmental input from many X developers. So depending on current affairs, the version of X on any distribution might be quite different from one release to another.