Five Free Distributed Computing Projects for your Idle  PC!
Distributed computing is one of the wonderful ways that you can use  your PC to contribute to more thoughtful, worldly causes than keeping  your room warm during a cloudy summer day. These projects, made up of  members from all corners of the world (even 
Maximum  PC's own forums), make use of your computer during its idle  periods. Whether they're come as a screensaver that launches after a set  period of time, or a background application that launches after a  certain period of CPU inactivity, these free applications divvy out the  tasks of a large, complicated project to a number of people at once. 
Why should you care? Because distributed computing is a nice way to  use a minimal amount of your system's resources--resources that you  wouldn't be using anyway--to contribute to something greater than  yourself. It's entirely altruistic in its purpose. Very, very few  distributed computing projects have some kind of monetary award attached  to the work, and you'd have to score a major knock-out in your  individual contribution to the project to see the result. That is, your  computer would have to be 
the one that finds the next huge  prime number, or major breakthrough in protein analysis, or something to  that effect. If you're in it for a reward, you might as well develop a  program that estimates lottery odds.
You'll find that entities like Maximum PC, amongst others, have teams  of people contributing to these distributed computing projects. It's a  great way to make friends and fellow geeks--in fact, I'd probably be  strung up by this site's forum folk if I didn't include a shout-out to  their work on the Folding@Home project. +10 
Light Side points  for you.
What it is: Stanford University says it best.  "Proteins are biology's workhorses -- its "nanomachines." Before  proteins can carry out these important functions, they assemble  themselves, or "fold." The process of protein folding, while critical  and fundamental to virtually all of biology, in many ways remains a  mystery. 
Moreover, when proteins do not fold correctly (i.e.  "misfold"), there can be serious consequences, including many well known  diseases, such as Alzheimer's, Mad Cow (BSE), CJD, ALS, Huntington's,  Parkinson's disease, and many Cancers and cancer-related syndromes."
Your goal? Use your computer to fold proteins (as a  part of 
Maximum  PC's team, if you so desire). You can set the program to use as  much or as little of your CPU as you desire, and you can even download  versions of Folding@home that make use of your GPU as well. Crazy,  high-performance stuff--for a good cause, of course. 
Download it 
here! 
What it is: Unlike chaos theory's Butterfly Effect,  popularized by the speculation that the beating of a butterfly's wings  could trigger a tornado in a distant location on the Earth,  Climateprediction.net has nothing to do with trying to plot out storm  predictions or anything super-fun like that. Instead, the program helps  scientists gain a deeper understanding of the variables that affect  future climate change. You're helping them to run the subtle tweaks in  their experiments on a grand scale, improving the ability of these  complex projections to accurately reflect future possibilities.
Still, no tornados. 
Download it 
here!
What it is: You're too late to earn the $100,000  cash prize, but the Electronic Frontier Foundation still has 
other monetary rewards up for  grabs. The catch? You have to be the person that helps discover prime  numbers with exceedingly large numbers of digits in them. Give 'er a  shot as part of the GIMPS distributed computing network--many, many  computers all contributing to the goal of finding increasingly larger  prime numbers. How large? The $100,000 winner's 3.0 GHz Intel Core 2  Duo-based PC took 29 days to run the calculations on the  12,837,064-digit prime number. That's quite a hefty number.
Download it 
here!
What it is: Insert your favorite science-fiction  theme here. SETI@home is a distributed computing project that uses the  computers of many to help scan the stars for signs of extraterrestrial  life. Although it's not your computer that's doing the star-searching  per se. Rather, you're merely helping to analyze the data that's already  been collected by radio telescopes. Who knows--you could be the one to  start a war with an 
intergalactic  species! 
Download it 
here!
What it is: Ever feel like turning your PC into a  particle accelerator? That's one mighty overclock. Sadly, you won't be  crashing real atoms into each other as part of the Muon1 project.  However, you 
will be helping to run simulations of the  following scenario: "You are simulating the part of the process where  the proton beam hits the target rod and causes pions to be emitted,  which decay into muons. These would then proceed to a storage ring and  decay into electrons and the neutrinos that are used for experiments. "
But don't think that you're just doing this for the heck of it. The  results of the distributed computing effort will affect the chances of  funding for the project's ultimate goal: firing particles through  Earth's interior, then measuring the changes to determine a neutrino's  mass. 
Just try not to create any black holes, eh? 
Download it 
here!
List of distributed computing  projects: