PC philanthropy is sharing some of the unused resources (mainly processor cycles) of your personal computer to benefit a social cause. For example, during the time that your computer is not working on applications that you're using, it can be working on some small part of a large-scale problem in medical research or the search for signals from outer space. Effectively, you and thousands of other PC users engaged in PC philanthropy become part of a kind of distributed supercomputer that is doing parallel processing.
Taking part in PC philanthropy requires that you download a small program from a Web site that is administering a project. In one example, this program comes with a screensaver included, so that when your computer is booted up and the screensaver automatically activated, the work program starts, too. It then uses your computer's processor cycles only when no other program in your computer is busy.
PC philanthropy is sometimes described as a form of peer-to-peer computing, in the sense that many Internet users are joined as peers in a common effort. One of the first PC philanthropy projects was the collective analysis of signals from outer space as part of the Search for Extraterrestrial Intelligence (SETI).