Wikipedia
TorChat
TorChat is a decentralized anonymous instant messenger that uses Tor hidden services as its underlying network. It provides cryptographically secure text messaging and file transfers. The characteristics of Tor's hidden services ensure that all traffic between the clients is encrypted and that it is very difficult to tell who is communicating with whom and where a given client is physically located.
TorChat is free software licensed under the terms of the GNU General Public License (GPL).