FVWM-Crystal
FVWM-Crystal aims to create an easy to use and powerful desktop.
... screened applications and the desktop in a manner similar to the application stack of the Amiga OS, which provides an innovative way to go around the desktop space, without compromising traditional X multiple desktop pages.
The core code was written by harnir Maciej Delmanowski with contributions from many other folks. The current developments are led by Dominique Michel.