The Mithral Client Server Software Development Kit (part of the Cosm project) allows developers to quickly and easily write large scale client-server applications including "distributed computing" and peer-to-peer types. Examples of what this will allow you to build with this technology are distributed.net, SETI@Home, Napster, Gnutella, etc.
Folding@home simulates protein folding. We do not entirely understand how proteins actually operate, but one important step is to study how proteins self-assemble or "fold." This is an extremely computationally intensive task since proteins take in the order of microseconds to milliseconds to fold, yet we can only routinely simulate over nanosecond to microsecond time scales. This system provides a new way to simulate protein folding that can break the millisecond barrier by dividing the work between multiple processors. Thus, with 1000 processors, we can break the millisecond barrier and help unlock the mystery of how proteins fold.