Tor

Tor (originally The Onion Router, no connection to the humor site/newspaper The Onion) is an anonymization protocol for the Web, using open-source software and a network of volunteer nodes which pass encrypted traffic through multiple hosts in order to make tracing difficult, though the NSA probably manages anyway. It is often used by people who distrust the government and its snooping, but ironically it has had much U.S. government involvement in its creation and funding.

Tor can be used as a proxy for anonymous use of normal Internet protocols and sites, or to access Tor-specific sites with ".onion" pseudodomains (which aren't regular domain names accessible via DNS, but which work only with Tor).

Links

 * Wikipedia article
 * Official site
 * Onion-Pi (Tor proxy server built using Raspberry Pi)
 * Make Tor go the whole hog