One of the most popular implementations of the X-Window system, X11 is supported by the Open Group X Project team.
A packet-switched data network.
A CCITT standard for mail formats.
X.400 A communications network tool. X.400 defines a message transfer protocol with advanced access control and accounting features
A directory system, X.500 is being superseded by more modern LDAP systems.
One of the earliest reliable file transfer protocols, Xmodem was written in 1977 by Ward Christiansen for use on the first BBS.
See also Ymodem and Zmodem.
A network-based GUI designed for Unix systems, there are thousands of free applications available as source code and compiled executables for X-Window compatible systems, including PC-based X-terminal emulators. X-Windowing systems are interesting in that they reverse the usual client- server metaphor.