Well, here’s an answer: volunteer computing.
How does it work? To participate you have to install client software which called BOINC (download page). Choose the version for your operation system and install. After it’s done you need to choose the project you want to participate in. Here are few examples.

SETI@home. The most famous distributed computing project. SETI stand for Search for Extra-Terrestrial Intelligence Home. Let's finally find them.

Einstein@Home. This project goal is searching through data for evidence of continuous gravitational-wave sources. Hosted by University of Wisconsin–Milwaukee and the Max Planck Institute for Gravitational Physics.

LHC@home. The project aim is to improve Large Hadron Collider (big deal, you know).

MilkyWay@Home  aims to generate 3d dynamic models of stellar streams in the immediate vicinity of Milky Way galaxy.

After you register your new project BOINC will download small portions of tasks to compute and it will start working on them. After the tasks are done BOINC will upload the results back to the project’s servers. You will get scores for each project.

BOINC should not use  too much resources from you computer. You can set it to work at night only, for istance. By the way, it shipped with nice screen saver.

Let’s make world better with BOINC and distributed computing!