i3 - A dynamic tiling window manager designed for X11, inspired by wmii, and written in C.
Fluxbox - Fluxbox is a window manager for X that was based on the Blackbox 0.61.1 code.
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
dwm - dwm is a dynamic window manager for X. It manages windows in tiled, monocle and floating layouts. All of the layouts can be applied dynamically, optimising the environment for the application in use and the task performed.