Academic
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This is where BOINC comes in. From your point of view, it's a program that runs on your computer that allows scientific computation programs to run when your CPU would otherwise be idle. That's about the nub of it: You and about a million others donate your idle CPU time to academic research groups.
There's also a social side to it. You can choose which projects you want to use your idle CPU cycles. There are currently about 50 active projects, ranging from advanced cosmology simulations to computer experiments on protein molecule folding dynamics to give insight into disease such as cancer. All of the active projects have flourishing forums where you can chat to like-minded people (you're all there because you have decided that project is worth supporting). There are also "crunching teams" you can join (e.g. BOINC UK), which themselves have active forums and usually have competitive "crunching drives" on the go - often against other teams in a spirit of, mostly, friendly competition.
Nice idea - how do I get started?
Simply download and install the BOINC software from the link below, then choose your projects.
BOINC - Compute for Science
BOINC always needs new contributors. I've been BOINCing for years - I hope you get into it as well, it's very satisfying being able to provide practical support to projects you believe in.
Some links to further reading ...
BOINC homepage at UC Berkeley
BOINC on Wikipedia
Some of my favourite projects ...
Cosmology@Home
Einstein@Home
LHC@home
PrimeGrid
SETI@home