The Tor Project is one of the simplest and easiest ways to browse the internet anonymously, but the network relies on volunteers to donate bandwidth. Instructables user fNX wanted to do their part, so they dedicated a Raspberry Pi as a Tor relay.
The Instructable takes a standard Raspberry Pi with Raspbian installed, and then walks you through the process of getting the network configured, and Tor installed. It's relatively simple provided you're familiar with Linux. The end result is a cheap relay and the fuzzy feeling that you're helping others browse the web anonymously. You can, of course, do this on any operating system, but the Raspberry Pi is a handy way to help out without bogging down your primary computer.
Raspberry Pi Tor relay [Instructables]