GridRepublic plugs you into a novel form of digital philanthropy: Volunteer Computing. From this website, you can download a bit of software which makes it possible to lend your PC's spare processing power to Cancer, AIDS, and Malaria study, to climate modeling, and to other vital causes. (You pick the beneficiary.)

By aggregating idle resources from large numbers of volunteers, we collectively create "virtual supercomputers": Computations that would take tens of thousands of years to run on an ordinary machine can be processed in just a few months.