Jitsi (previously SIP Communicator) is a cross-platform VOIP, videoconference, desktop sharing and chat client.
Protocols supported include SIP, XMPP/Google Talk/Jabber/Facebook chat, AIM/ICQ, Windows Live, Yahoo! Messenger and Bonjour.
Other features include: Call recording, Call & chat
... [More] encryption, Noise suppression, Echo cancellation, File transfer, multi-user chat, Desktop streaming, Presence, Conference calls, Integration with Microsoft Outlook and Apple Address Book, Support for LDAP directories, Support for Google Contacts, On-line provisioning, Systray notifications, IPv6 support, Spell checker and many more. [Less]
BigBlueButton is an open source web conferencing system for distance education.
BigBlueButton supports sharing of slides (PDF and PPT), video, whiteboard, chat, voice (using Freeswitch or Asterisk), and desktops. It's built using over fifteen open source components, runs on Mac, Unix, and PC
... [More] computers, and is backed by an open source community that cares about good design and a streamlined user experience.
Webcam, Presentation, Integrated VoIP, Desktop Sharing