ScatterChat

ScatterChat is a secure instant messaging client designed for non-technical users who require secure and anonymous communications. Our typical end-users include human rights and democracy advocates operating in hostile territory. ScatterChat is also a valuable tool for anyone requiring secure communications.

It is based upon the Gaim software, provides end-to-end encryption, integrated onion-routing with Tor, secure file transfers, and easy-to-read documentation.

ScatterChat's security features include resiliency against partial compromise, immunity from replay attacks, and limited resistance to traffic analysis... all reinforced through a pro-actively secure design.

http://www.scatterchat.com