World Community Grid
I run a program from World Community Grid on my computer. The Grid is a large community of computers (people) who have excess computing time that is donated for doing parts of large-scale computations.
Right now there are 11 active projects working on the grid. I am signed up for the Computing for Clean Water program. To date this project has accumulated over the equivalence of over 33,000 days of computer time toward the project.
If you are interested in finding more about this great program, check out this link.
The blue graphics page does not normally show, but you can bring it up to see what is going on. I am donating 40% of my computing time to the project. I hardly notice any slowness in my personal operations.