Stumpwm attempts to be customizable yet visually minimal. There are no window decorations, no icons, and no buttons. It does have various hooks to attach your personal customizations, and variables to tweak.
The homepage is located at http://www.nongnu.org/stumpwm.
Stumpwm's focus is on doing for windows what Emacs does for files and buffers: smooth customizable control. I find overlapping windows introduces needless clutter, which is why stumpwm tiles windows. Rather than flipping through a clutter of windows, stumpwm , presents windows in a numbered list. Much more civilized. And finally, like Emacs, everything is done with keystrokes (yes Emacs does allow you to use the pointer, and perhaps if there is a need stumpwm will too) which allows for seamless task switching between file editing and window navigating.
Male has put together a video featuring stumpwm's new features: http://www.archive.org/details/TheStumpWMExperience