The World Community Grid is an organization attempting to create the world's largest public computing platform. This supercomputer is made up of members' computers from around the world, and computing time is donated to humanitarian research projects that would not otherwise go forward due to the cost of supercomputing time. Results from the efforts are made public so researchers all over the world can use them.
Here's how it works: you download a small program that runs when your computer is idle. Your computer will perform calculations on the data and then send it back to the server, where it is merged into the results from everyone else. This will not interfere with your computer's response time; the program will only use CPU cycles that you were not going to use anyway. So you won't see any slowdown or have to wait for a segment of data to be completed. You use your computer as normal and the WCG program will run when it can.
Currently the World Community Grid is working on two projects: FightAIDS@Home and the Human Proteome Folding Project, which determines how human proteins fold. With a better understanding of how proteins fold, scientists hope to cure cancer, HIV/AIDS, SARS, and malaria.
For more information go to worldcommunitygrid.org