Proper noun
X11
(computing) A windowing system for bitmap displays, common on Unix-like operating systems.
After Sun canceled NeWS, DUX Software contracted Hopkins to rewrite the HyperLook user interface in TCL/Tk for X11, and he developed a multi-player networked user interface using the X11 protocol. Source: Internet
Apple originally ported X to OS X in the form of X11. Source: Internet
Details YaST is also available without X11 (with ncurses YaST is free software that SUSE has made available under the GPL in 2004. Source: Internet
APE's authors claim to have used it to port the X Window System (X11) to Plan 9, although they do not ship X11 "because supporting it properly is too big a job". Source: Internet
Because OS X can optionally use an X11 server, porting GIMP to OS X is simpler compared to creating a Windows port. Source: Internet
Alpha testing of the software started in February 1987, beta-testing in May; the release of X11 finally occurred on 15 September 1987. Source: Internet