Acronym: The Onion Router
From the homepage:
- Tor is a connection-based low-latency anonymous communication system which addresses many flaws in the original onion routing design.
- "The simple version: Tor provides a distributed network of servers ("onion routers"). Users bounce their TCP streams (web traffic, FTP, SSH, etc.) around the routers. This makes it hard for recipients, observers, and even the onion routers themselves to track the source of the stream."
- "The complex version: Onion Routing is a connection-oriented anonymizing communication service. Users choose a source-routed path through a set of nodes, and negotiate a "virtual circuit"; through the network, in which each node knows its predecessor and successor, but no others. Traffic flowing down the circuit is unwrapped by a symmetric key at each node, which reveals the downstream node."
Currently, Tor development is supported by the Electronic Frontier Foundation. Tor was initially designed and developed as part of the U.S. Naval Research Laboratory's Onion Routing program with support from ONR and DARPA. The Onion Routing implementation tries to solve various existing flaws in the original Onion Routing implementation.
This service is active, working, currently in use, and has grown to hundreds of thousands of users. Tor currently has over 1,000 active routers from all over the world.