xmmstcl lets you control XMMS playback, skip, pause, change the playlist, change skins, and do everything else provided by the xmms_remote_* methods, which is almost everything from the standard user interface. It also has some things not available there, such as "XMMS onchange" which lets your Tcl/Tk application know when something happens in the player. The companion "TkPlayer" has samples for the most important functions and will keep XMMS busy by generating random playlists with songs that you haven't heard in a while.
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. xmonad is extensible in Haskell, allowing for powerful customisation. Custom layout algorithms, key bindings, and other extensions may be written by the user in config files. Layouts are applied dynamically, and different layouts may be used on each workspace. Xinerama is fully supported, allowing windows to be tiled on several physical screens.
If a USB mouse is declared the core pointer, X won't come up without it, AllowMouseOpenFail notwithstanding. If it has SendCoreEvents set, xmodmap pointer = ... will no longer remap its buttons, as it only works on the primary pointer. xmootmap is a bare bones command line tool that lets you remap buttons on secondary pointers, and is aimed at laptop users with funky mice. Intended use is mostly from ~/.xinitrc.
Xnetintf is an X Windows application that manages network interfaces. The current interface state is depicted through a series of bitmaps, and a mouse click in the window initiates a state transition. Xnetintf uses a per-interface configuration file to supply commands that check and toggle state, as well as a program to run after the state change completes. A command line interface is also supported.