Open source distributed computing (Score 1)

As far as I know, none of these distributed computing efforts release their source code. I understand that they have reasons for this, but I still have no intention of running any code on my machine for which I cannot see its method of operation; especially given the recent scare over Real sending back 'interesting' data from their servers.
So, are there any projects which do have full open source clients? I'm not necessarily so worried about their freeness or otherwise, I'd just like to know exactly what they're doing.