Jitsi - Video Calls and Chat
Jitsi provides Secure Video calls, Conferencing, Chat, Desktop sharing, Instant Messaging, File transfer support for your favorite OS and IM network. Jitsi lets you connect to Facebook, GoogleTalk, XMPP, Windows Live, Yahoo!, AIM, and ICQ so that you can chat to all your friends in the simplest possible way. It supports IPv6, Secure calls with zRTP, Call history, Call hold etc.
It is well integrated with Microsoft Outlook, Apple Address Book, Google Contact, LDAP directories.