My three DC-projects
I am running quite a few software projects, in particular I am talking about the various DC-projects that I participate in ("DC" stands for "Distributed Computing"); please click over to Distributed Computing.info that nicely list most if not all the projects, the current and the past ones. Distributed computing is a technique which tries to solve problems by splitting the task between different computers (usually its volunteer-based, see the Distributed-Computing.doc file, which is a nicely-written proposal that you can make to your boss, your company in general etc.); when each such sub-task is solved, the results/solutions are gathered and compiled together to provide the answer to the original problem. The thing is that most computers use only between 5% and 10% of their CPU capacity with the rest of the time CPU sitting idle. If you are running Windows operating-system, open the Task Manager program and see for yourself.
Anyways, personally I participate in the following projects: BeWeS MouseTracker, SETI@Home, GIMPS/Prime95, and Folding@Home. While in general, a typical participation in most of them involves downloading and installing a client programs on your home/business or whatever computer. This client programs then fetches Work Units (WUs) from a centralized server. Once the WU is processed by the client machine, the result is then returned to the server in exchange for a new Work Unit. But the most important thing is that distributed computing projects are designed to harvest only the unused CPU-cycles to perform the mentioned useful computational tasks, i.e. they do their work only when the computer's CPU is IDLE (in other words, they make use of the so-called IDLE CPU-cycles), i.e. when computer doesn't use almost any power at all, so they have no impact on overall system's performance whatsoever.
Lately I am running only Folding@Home client since the processing of Lucas-Lehmer primality test for number M32011367 (yeah, it was not a prime) in Prime95 project ("GIMPS" above stands for "Great Internet Mersenne Prime Search") took me more than a year to finish it on my old computer, and this is definitely much too long for my taste. Therefore I've decided to rather start processing only F@H project's WUs again, at least until I get faster computer, heh, or until I convince a friend of mine to start processing some for F@H project under my name. I might continue with trial factoring of numbers (which is much faster), but this is something different, and you are not actually searching for prime numbers, just eliminating the easy ones that are not primes. For much more information and my personal statistics, please head on to the "projects" page on my main computing related website.