Freedesktop.org

(As of: 29 April 2013)

freedesktop.org is  / open discussion software projects working on interoperability and shared technology for X Window System desktops. The most famous X desktops are GNOME and KDE, but developers working on any Linux/Unix GUI technology are welcome to participate.

freedesktop itself is host to numerous other wikis (all MoinMoin) for various subprojects, including:
 * Xorg X window server and libraries
 * Cairo graphics library
 * XCB Xlib replacement library
 * The nouveau wiki for programmers trying to produce open-source 3D drivers for nVidia graphics cards.
 * The DRI wiki maintains a list of graphics cards that have DRI drivers available, and supports programmers improving DRI. DRI, the 'direct rendering infrastructure', allows direct access to graphics hardware under the X Window System.
 * PulseAudio wiki

See also X.Org, the X window wiki.