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.
AfterStep is a Window Manager for X which started by emulating the NeXTSTEP look and feel, but which has been significantly altered according to the requests of various users. Many adepts will tell you that NeXTSTEP is not only the most visually pleasant interface, but also one of the most functional and intuitive out there. AfterStep aims to incorporate the advantages of the NeXTSTEP interface, and add additional useful features.
Ion is a tiling (no overlapping windows) window manager that also has PWM-style tabbed frames which can contain multiple client windows. These features help to keep windows organized and to switch quickly between them. Ion was designed primarily as an efficient and unobtrusive window manager for users who prefer the keyboard.