Tor is a network of virtual tunnels designed to improve privacy and security on the Internet by routing your requests through a series of intermediate machines. It uses a normal proxy server interface so that ordinary Internet applications like web browsers and chat programs can be configured to use it. In addition to helping preserve users' anonymity, Tor can help evade firewall restrictions. Tor's hidden services allow users publish web sites and other services without revealing their identity or location. For a free cross-platform GUI, users recommend Vidalia. Remember that Tor exit nodes are sometimes run by malicious parties and can sniff your traffic, so avoid authenticating using insecure network protocols (such as non-SSL web sites and mail servers). That is always dangerous, but particularly bad when routing through Tor.
For downloads and more information,
visit the Tor homepage.