Einstein@Home: donate your computer's idle time to search for pulsars and gravitational waves

Einstein@Home uses your computer's idle time to search for weak astrophysical signals from spinning neutron stars (pulsars) in data from the LIGO gravitational-wave detectors, the MeerKAT radio telescope and the Fermi gamma-ray satellite, as well as archival data from the Arecibo radio telescope. The project page says it has over 500,000 volunteers; you can join with the Join now button, and there is no application deadline.