The Einstein@Home project uses the idle resources of a distributed network of computers to search for pulsars, which are spinning neutron stars. The software analyzes data gathered by the LIGO and GEO gravitational wave detectors.
From the Einstein@Home Screensaver description:
The Einstein@Home Screensaver has a number of elements related to current efforts to detect gravitational radiation from periodic sources such as pulsars. The primary element of the screensaver is a rotating celestial sphere showing the known constellations, along with the current zenith positions of three gravity wave detectors. The positions of the detectors relative to the stars changes periodically over a 24 hour period. If you went to one of the detector sites, the stars visible directly overhead at any time are the same ones that appear next to the detector on your screensaver. (This assumes of course that your computer's time and timezone are correctly set!) Also shown are the positions of the known pulsars and supernovae remnants, and a marker indicating the positions being searched as the calculations proceed. When the graphics are shown in a separate window (not as a screensaver) the user can control the display with the mouse and keyboard.