Jitsi

The Jitsi interface is reminiscent of older chat clients such as Empathy, but is more usable. You begin by logging into an XMPP or a SIP server account, or both. The best feature of Jitsi is its OTR implementation, which enables you to have secure private conversations with your contacts. However, all conversations with your contacts on either networks are unsecured by default. You must use the Secure chat pulldown menu in the chat window to bring up encryption options. As the tool takes your privacy quite seriously, it requires users to share a secret or verify their fingerprint for authentication. As an added security feature, you can even stop recording the chat session with a single click from within the chat window itself. Even better, it similarly enables you to initiate secure audio and video calls with your contacts.