Scwm is the Scheme Configurable/Constraints Window Manager, a window manager with a powerful dynamic configuration language based on Guile Scheme. Scwm has many, many advanced features, often implemented in the configuration language itself.
awflwm is a fork (and extension) of flwm that strives to remain a little more current than flwm (it appears that Bill hasn't had much time for flwm in recent years).
The Wimp is a (yet another) generic window manager for X11. It provides an abstract and reusable API for window management which allows for completely new window management paradigms. It combines highest flexibility, usability and standards compliancy.