Sawfish (the window manager formerly known as Sawmill) is an extensible window manager using a Lisp-based extension language. All window decorations are configurable and all user-interface policy is controlled through the language. Its aim is to manage windows in the most flexible and attractive manner possible. As such it does not implement desktop backgrounds, application docks, or other things that may be achieved through separate applications. Sawfish is mostly GNOME-compliant; almost all configuration may be made through a graphical interface.
FVWM-Crystal aims to create an easy to use, pretty, but also powerful desktop environment for Linux or other Unix-like operating systems. It uses the following programs: FVWM as a window manager and "main core"; different ways to provide icons on the desktop including support for many file managers and custom commands; xterm, aterm, mrxvt, or urxvt as terminal emulators; MPD or XMMS2 as music players (there's built-in support for controlling these programs), and several other tools for different functions, like setting a wallpaper or taking screenshots.
spectrwm is a minimalistic tiling window manager that tries to stay out of the way so that valuable screen real estate can be used for much more important stuff. It has sane defaults and does not require one to learn a language to do any configuration. It was written by hackers for hackers and it strives to be small, compact, and fast.