X Windows was released in 1984 and has been known as X11 or X since 1987. It is a Unix windows system not an operating system. X Windows did not have a GUI specification and different companies wrote their own windows systems based on X (Sun wrote XView and OpenWindows and the Open Software Foundation wrote Motif) before CDE (Common Desktop Environment) was released in 1993 as a collaboration of OSF, IBM, HP and Sun. The games on this page were written for X11 on Unix systems, in particular SunOS (1982), System V (1983) and HP-UX (1984).