WMpop is a Window Maker dock app that monitors a local (mbox format) or POP3/APOP mailbox to inform you when mail arrives. It displays the amount of mail in the mailbox (or unread mail if checked in the preference screen), a scrolling text with the email address of the senders (only for local mailbox at the moment) and a status led, indicating mail checking progression and errors. It can be configured and personalized (icons and sound) via a GTK+ GUI.
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.
aewm is a minimalist window manager for X11. It has no nifty features, but is light on resources and extremely simple in appearance. It should eventually make a good reference implementation of the ICCCM. A few separate programs are included to handle running programs, switching between windows, etc.