Geo TCP is an xscreensaver hack that displays TCP connections on a map of the world. This will require pyxsshack (available here) and the python-geoip with the GeoIPCity (or Lite version) database.
Tempest is an xscreensaver hack based on a physical model where particles are attracted to their 8 neighbors. With some tweaking, it can produce some very neat effects.
GScreen is a session manager for the GNU Screen program. It is designed to work with GTK/GNOME. Note you will also need to install pyeggtrayicon
Tortuga is a docking window manager. This is a sort of combination of tiling window managers with the desktop metaphor. Applications can be docked together to form a layout. This is useful for organizing applications working on the same project, or for example, docking the GIMP toolbar to a picture you're editing. WARNING: This software is in early alpha (ie. it runs poorly and crashes often :D )
You will need to create/edit /etc/tortuga.conf for this WM to work at all. Try the following:
frame_active_primary 252 175 62 255
frame_active_secondary 255 255 255 31
dock_active_primary 238 238 238 255
pyxsshack provides Python binding to easily create OpenGL-based XScreenSaver hacks.
pyeggtrayicon provides Python bindings to the tray icon from libegg. Note that this project includes the tray icon from libegg; you do not need to have libegg installed. This one also includes a patch to enable transparency.