IceWM is a window manager for the X Window System (freedesktop, XFree86). The goal of IceWM is speed, simplicity, and not getting in the user's way.
The Official IceWM Website: http://www.icewm.org
IceWM at Window Managers for X: http://www.xwinman.org/icewm.php
An article by an IBM developer: http://www.osnews.com/story.php/7774/IceWM--The-Cool-Window-Manager/page1/