BOINC is an open source software platform to allow distributed computing projects like SETI@Home and Climateprediction.net (CPDN) which use volunteered computer resources to run. Why leave a computer idle when it could be doing something beneficial?

You can participate in several projects, ensuring that your computer will be kept busy even when one project has no work. You can control how your resources (such as computer time and disk space) are divided among these projects.