ScatterChat
ScatterChat is a secure instant messaging client. From the press release:
ScatterChat is unique in that it is intended for non-technical human rights activists and political dissidents operating behind oppressive national firewalls. It is an instant messaging client that provides end-to-end encryption over the Electronic Frontier Foundation-endorsed Tor network. Its security features include resiliency against partial compromise through perfect forward secrecy, immunity from replay attacks, and limited resistance to traffic analysis, all reinforced through a pro-actively secure design.
A nice application of Tor.
EDITED TO ADD (8/8): There are flaws in the protocol. There’s an advisory on one of them.