SETI...the Search for Extra Terrestrial Intelligence. NASA originally ran this project, but funding was axed as the US Government deemed it a waste of time & resources. The gauntlet got picked up by Berkeley University, and they had a seemingly divine piece of inspiration. The project required computer resources way beyond a university IT budget. Super computing power was needed. The US Government wasn't interested, but what about the public? In particular, the Star Trek fans, the geeks, the bespectacled spotty kids with no mates? Get enough of them to "donate" unused computing power, and you have the worlds largest, most powerful computer. The public answered the call and computing history was made. SETI is now, effectively, the largest supercomputer on Earth.

 
I ran SETI "classic" from April 2004 to April 2005. 10000 work units crunched, but I'm sorry to say not one alien found. Not even a little one.
Now I'm running the new BOINC (Berkeley Open Infrastructure for Network Computing) version of SETI. Hoping to find my alien sometime soon - page will be updated when I do so you know where you'll hear it first ;)