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.
dvtm brings the concept of tiling window management, popularized by X11-window managers like dwm, to the console. As a console window manager, it tries to make it easy to work with multiple console based programs like vim, mutt, cmus, or irssi. dvtm is intended to be used where X11 isn't available or over SSH. In conjunction with dtach, it can be seen as a lightweight alternative to GNU screen.
dwm is a fast and simple window manager for X11. It manages windows in tiled and floating layouts. Either layout can be applied dynamically, optimizing the environment for the application in use and the task performed. Windows can be tagged with one or multiple tags. Selecting certain tags displays all windows that are accordingly tagged. dwm is the little brother of wmii.
wmii is the next generation of wmi. It is a highly customizable keyboard-and-mouse-driven X11 window manager that supports conventional, tabbed, and tiled window management with low memory usage and vi-like user interaction. Due to a complete rewrite, it is highly modularized and uses a new configuration and inter-process communication interface, which is oriented on the 9p protocol of the Plan9 operating system.
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.
WMI is a lightweight window manager for X11 which attempts to combine the best features of larswm, ion, evilwm, and ratpoison into one window manager. It supports both the conventional way of managing windows in a overlapping manner and the screen-alike way of managing windows in a non-overlapping fashion.