XScreenSaver offers a couple of hundred different screen savers together with a framework for blanking and locking the screen. The screen savers are known in the software’s development as ‘hacks’ and range from simple 2D effects to 3D demonstrations of complex mathematical principles, to simulations of other computer systems, space phenomena, to re-creations of artifacts and effects from movies such as Tron, Star Wars and The Matrix.

Source: LXer – Linux Candy: XScreenSaver – Framework and collection of screensavers