FVWM

Fvwm (F? Virtual Window Manager for X11) is a window manager for X11. It is designed to minimize memory consumption, provide a 3D look to window frames, and a virtual desktop. Fvwm is now in the portage tree and you can install it by using:

Use flags
The following USE flags are supported by package:

Configuration for fvwm
Fvwm Configuration file is ~/.fvwm/config.

Links
http://en.gentoo-wiki.com/wiki/FVWM/Configuration