The Berkeley Open Infrastructure for Network Computing (BOINC) is a non-commercial middleware system for volunteer and grid computing. It was originally developed to support the SETI@home project before it became useful as a platform for other distributed applications in areas as diverse as mathematics, medicine, molecular biology, climatology, and astrophysics. The intent of BOINC is to make it possible for researchers to tap into the enormous processing power of personal computers around the world.
You can download BOINC client for your computer here: http://boinc.berkeley.edu/download.php. After installation consider joining some project, for example, I am taking part in Milkyway@home. You can also consider join some project team. For example, I am a member of team Ukraine: http://milkyway.cs.rpi.edu/milkyway/team_display.php?teamid=120
In June 2011 I entered the top 10 contributors of team Ukraine by recent average credit (RAC).
In June 2012 I entered the top 3 contributors of team Ukraine by recent average credit (RAC).