Zeta Desktop Environment (ZDE) is an X11 window manager and tools with enhanced usability and features for advanced users and developers. Some of its current sub-projects include imp, a library of core functions such as linked lists, zwl, a simple widget toolkit and light X11 wrapper, and zimwm, the window manager.
libDockApp is a simple library for easily writing Window Maker dock applications, also known as dockapps (those that only show up in the dock). It is very limited and can only be used for dockapps that open a single appicon for each process in only a single display, but this seems to be enough for most, if not all, dockapps.
Tom's Virtual Tab Window Manager (tvtwm) is a superset of the X11R5 release of twm, initially written by Tom LaStrange. The major benefit of tvtwm over twm is the "Virtual Desktop". This allows you do define a substitute root window that is larger than your display area. This new virtual root window is the parent for all of your X clients. tvtwm provides a "Panner" which will let you see a scaled down representation of the whole virtual desktop. Using this panner and keys bound to functions added to tvtwm, you can move around this desktop while having your physical display showing only part of the whole desktop.