From wikipedia:

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. (…)

A signature graphic file, dynamically generated by BOINCStats, displays the credits gained by a volunteer on the various projects that run on BOINC.

BOINCStats.com user signature graphic

BOINC: http://boinc.berkeley.edu (download)
BOINCStats: http://www.boincstats.com

Citizen science: People power (Nature)
The people’s pulsar: Volunteer computing project discovers neutron star (ScienceNews)