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.
fpcbol is a desktop user interface written for children and people who want simplicity and speed. It is designed to be as beautiful and simple as possible. It has no menus, just icons to click. It features parental control for children. It has been tested successfully on Debian, Mandriva, and Gentoo. It works well on computers with low system resources (such as a 500Mhz Pentium). 3D acceleration is necessary for the optional transparency feature.
echinus is a lightweight window manager for X based on dwm's source code. It manages windows in tiled, maximized, and floating layouts. It is extremely small, rather fast, and supports Xft. It features nice titlebars, multiple desktops, theming support, a simple configuration file, the ability to switch desktops with the mouse wheel, X bitmaps for title buttons, and true transparency support (through xcompmgr). There is no need to recompile or restart X to change its configuration.
subtle is a grid-based manual tiling window manager with a strong focus on easy but customizable look and feel. In comparison to other tiling window managers, subtle has no automatic tiling of the screen size in any way. Instead, windows are arranged according to positions inside of a grid. These positions are called gravities.