BOINC is an open source application with which you can connect to a number of projects and share your computer’s resources. At BOINC’s startup, it will display a list of all the projects you can participate in. Select one or simply type in the url if it isn’t included. Afterwards, I’d suggest looking into the preferences to set BOINC to use your computer only when it is idle, such as overnight. Don’t forget to leave it connected to the Internet though.