From Telecomix Crypto Munitions Bureau
"Cryptocat lets you instantly set up secure conversations. It's an open source encrypted, private alternative to other services such as Facebook chat. | Messages are encrypted inside your own browser using AES-256 and 4096-bit asymmetric keys. Encrypted data is securely wiped after one hour of inactivity. | Cryptocat also runs as a Tor hidden service (http://xdtfje3c46d2dnjd.onion) and works on your iPhone, Android and BlackBerry." -- Crypto.Cat
There is also now a #Cryptocat channel on Telecomix IRC and a Pad ( http://pad.telecomix.org/cryptocat ) with links to the Cryptocatroom (url subject to change).
Notes: Appears not to work on Android Gingerbread default browser. It is possible generate keys and even view the chat but impossible to type due to keyboard/AJAX issues (?).