A large majority of volunteer computing projects are based on freely available middleware software called BOINC (Berkeley Open Infrastructure for Network Computing).
BOINC was originally developed to support the SETI@home project. It provides server software that lets scientists create volunteer computing projects and client software that lets volunteers participate in any combination of these projects.
BOINC is used by projects from institutions across the globe for applications as diverse as mathematics, medicine, molecular biology, climatology, and astrophysics.
The types of applications are varied and can involve computer-intensive analysis of large data sets (e.g. Einstein@home project analyses Petabyte-scale data). Some applications may require computer power for producing complex simulations; for example climateprediction.net is using volunteer computing to predict and modelling the earth’s climate up to 2100.
It takes only takes a few minutes for volunteer to download and run applications on their own computers. After installing the software, you can connect it to as many projects as you like.