Pidgin

Pidgin is an easy to use, multi-protocol chat client client used by millions. Connect to AIM, MSN, Yahoo, XMPP, and more chat networks all at once. It has built-in support for NSS, offering client-to-server message encryption for protocols that support it. The program is extendable through plugins, including "Off-the-Record Messaging" and Pidgin encryption, providing end-to-end message encryption.