Fluxbox - Fluxbox is a window manager for X that was based on the Blackbox 0.61.1 code.
IceWM - icewm home page . Bug Tracking. If you have a patch, a bug report or a feature request to submit, please do so at the icewm project page at SourceForge.
flwm - Productivity and Qt
Openbox - Openbox is a highly configurable, next generation window manager with extensive standards support.
Window Maker - Window Maker is a free and open-source window manager for the X Window System
i3 - A dynamic tiling window manager designed for X11, inspired by wmii, and written in C.