Folding@Home

Folding@Home(aka FAH) is a distributed computing project. To quote from their website, FAH is a distributed computing project for simulating protein dynamics, including the process of protein folding and the movements of proteins implicated in a variety of diseases. Folding@Home involves you donating your spare computing power by running a small client on your computer. The client then contacts the Folding@Home Work Assignment server, gets some workunits and runs them, You can choose to have it run when only when your system is idle, or have it run all the time.