Xswarm is an X11 client that animates a group of line segments. One line is called the wasp and the others are the bees. The bees constantly accelerate toward the wasp, forming a cute pattern that continually changes. Because Xswarm is commonly left running in the root window, it was made possible to control how much cpu time it uses with the -d option. If a mouse button is pressed while the pointer is in the xswarm window, the wasp becomes controlled by the mouse.
Control is released when the mouse button is pressed again.
The parameters that affect behavior of the swarm are controllable by the user through command line parameters. One of the recently added capabilities of Xswarm is screen saving. As far as I know, this is the first example of an X screen saver other than the one built into the server. By screen saver, I mean a program that does not require a signal from the user to take over the screen.