Currently the largest distributed effort with over 1,800,000 users. Cosm - Cosm provides an infrastructure for true distributed computing projects. This includes applications as well as APIs for users to design and build their own projects. Net - Newest distributed computing group. They are currently working on the Gamma Flux Project, which is useful in designing safer containers for nuclear waste.
Membership is free, with no obligations.
Java based distributed scientific simulations - A small site with an objective to use Java as a base for distributed scientific simulations. A Worldwide Virtual Computer - A worldwide virtual computer. PiHex - PiHex is a distributed computing project that is calculating specific parts of Pi using computers from all over the world. This group started developing their project in 1999. They want to use your idle computer cycles for money.