http://en.wikipedia.org/wiki/CryptocatCryptocat is an open source web and mobile application intended to allow secure, encrypted online chatting. Cryptocat encrypts chats on the client side, only trusting the server with data that is already encrypted. Cryptocat is offered as an app for Mac OS X or as a browser extension for Google Chrome, Mozilla Firefox, Apple Safari, Opera and as a mobile app for iPhone.
Cryptocat's stated goal is to make encrypted communications more accessible to average users. The chat software aims to strike a balance between security and usability -- offering more privacy than services such as Google Talk or Internet Relay Chat, while maintaining a higher level of accessibility than Pidgin