Razor-QT is a desktop environment for Linux (and probably other *NIXes running X) that aims to be fast, easy to use, simple, and does not require much in the way of system resources so it can be used on older machines. Uses Trolltech's QT libraries. Contains everything you'd expect of a fully operational desktop, from the panel at the bottom of the screen to the desktop manager and a system configuration app. Need a window manager but anything Desktop-compliant will work (most people use Openbox).
linux -desktop -open-source -qt -X -window-manager -software