The W window system is a discontinued windowing system and precursor in name and concept to the modern X window system.
W was originally developed at Stanford University by Paul Asente and Brian Reid for the V operating system. In 1983, Paul Asente and Chris Kent ported the system to UNIX on the VS100, giving a copy to those working at MIT's Laboratory for Computer Science.
In 1984, Bob Scheifler of MIT replaced the synchronous protocol of W with an asynchronous alternative and named the result X.
Since this time the X window system has gone through many fundamental changes and no longer bears any significant resemblance to W.
Other W window systems
There exists more than one window system named W. In 1995 Torsten Scherer released a suite dubbed W1R3; it has since been modified by Eero Tamminen and released as W1R4 under the GNU Lesser General Public License for the libraries, and the GNU General Public License for the rest. This work postdates both W and X by many years, and has no code in common with either. It was used in the Yopy Linux PDA.