A personal computer is great at crunching numbers - actually, when you reduce it to the basics that is all computers really do. Most home computers are also idle a good part of the time, and many folk leave them on 24/7 - wouldn't it be nice to do something useful with all that spare computing power?
There are several ways you can use your computer's idle time to do calculations that can help contribute to research in various fields. Folding@home helps with research into protein folding in order to better understand some major diseases like Alzheimer's, cancer, etc.
This type of activity is referred to as distributed computing, as the workload is shared (distributed) across many individual computers - turning home computers into a sort of cloud supercomputer.
Let me invite you to start folding, and to join the OldGoatGuide team (number 229514) - of course, you don't have to join any team to start folding, and everything is otherwise anonymous.
I have actually been folding for a couple of years, but only recently created the OldGoatGuide "team", so it will be interesting to see if anyone joins up.