X Window System
A graphical windowing system that was initially developed on minicomputers and therefore works on a client/server concept, commonly shortened as X11. The original idea was that the application ran on a server or minicomputer of some sort and the PC/workstation/terminal acted as a graphical terminal to the program, this made a lot of sense at the time as servers had considerably more computing power than workstations and you can still split X Window applications up in that way, but it is more common to see the system used as simply a windowing system or a primitive GUI with the application, X11 server and X11 client all running on the same computer.
This of course means that the X Window System is as much a networking protocol as it is a windowing system, but considerable time was spent in the design stages of the system to minimise the amount of information needed to transfer between the X11 server and client, and in this respect it is not dissimilar to modern GUI remote access protocols, if a bit more limited in scope. For this reason it is common to see the X11 system classified under networking, especially on older systems, or ones with a long history.
The X Window System is primarily used on UNIX like systems but is or has been available for systems as diverse as embedded microkernel systems, DesqviewX and Microsoft Windows. On OS/2 and MS Windows it is primarily used to simplify the porting of applications from UNIX like systems, so is almost used as a graphics library rather than as a windows system, but it is also possible to use it as it was originally intended on those systems, or use it as a graphics terminal.
It should be noted that in X Windows parlance the terms "Client" and "Server" have the exact opposite meaning to what the rest of the world thinks they mean.
Implementations for OS/2
- EverBlue - A project to create a native OS/2 graphics library version of X11
- Hummingbird Exceed - Native PM X11 server - Commercial - Discontinued
- HOBLink X11 - Native PM or separate OS/2 Server/client
- PMX - From IBM - Native X11 server - Discontinued
- XFree86 - Port of the XFree86 client/server - Open source - Discontinued
Implementations for DOS
- DesqviewX - Commercial - Discontinued
- GSS*X/386 - Workstation terminal software similar to PC-Xview that ran on 80386 PCs - Commercial - Discontinued
- PC-Xview - DOS based X-Windows terminal emulator for 286/386 PC's - Commercial - Discontinued
- The Open Group's X Windows page - The Open Group handles the standardisation of the X Window System
- Sebastian Wittmeier: Running X11 Applications on the OS/2 and eCS Desktop - An old but useful presentation, primarily about EverBlue but does mention other possibilities.
- Michael Johnson: X-CUA: the X Window System under VM - Published as part of Proceeding of The REXX Symposium for Developer and Users May 18-20, 1993, page 96 (page 102 in the PDF version).