This tool lets you programatically (or manually) simulate keyboard input and mouse activity, move and resize windows, etc. It does this using X11's XTEST extension and other Xlib functions.
xmonad is a tiling window manager for X. Windows are arranged automatically to tile the screen without gaps or overlap, maximising screen use. Window manager features are accessible from the keyboard: a mouse is optional.
wmii is a small, dynamic window manager for X11. It is scriptable, has a 9p filesystem interface and supports classic and tiling (acme-like) window management. It aims to maintain a small and clean (read hackable and beautiful) codebase.