Jitsi

Jitsi is a communications program that allows you to chat securely using well-supported protocols like SIP, XMPP / Jabber, AIM / ICQ, Windows Live, Facebook and Yahoo. You can also make audio and video calls and share or stream your desktop to someone else. Conference calls and call recording are also possible. Most importantly, all of these features can be used together with a strong encryption.

Chatting securely with other rights advocates

Allows you to integrate various communication protocols into one program

Windows, Mac OSX, Linux
FOSS
Easy