Leading Open Source Video Conferencing software
Ekiga (formely known as GnomeMeeting) is an open source SoftPhone, Video Conferencing and Instant Messenger application over the Internet.
It supports HD sound quality and video up to DVD size and quality.
It is interoperable with many other standard compliant softwares, hardwares and service providers as it uses both the major telephony standards (SIP and H.323)
BigBlueButton is the rising star of open source video conferencing. It supports sharing of slides (PDF and PPT), video conferencing , whiteboard, chat, voice (using Asterisk or FreeSWITCH), and desktops.
Jitsi (formerly SIP Communicator) is an audio/video conferencing and chat communicator software that supports protocols such as SIP, XMPP/Jabber, AIM/ICQ, Windows Live, Yahoo! and many other useful features.
Jitsi is Open Source / Free Software, and is available under the terms of the LGPL.
Other Open Source Video Conferencing software
VMUKTI is Social, Web 2.0, SaaS, Peer-to-peer, & VoIP Open Source multi-Party Conferencing (like video and web conferencing WebEx) Broadcasting , Collaboration And CMS platform for Web & Mobile users Video/ Audio/ Presence & Content.
OpenMeetings is a free open source video and web conferencing software. You can use your microphone or webcam, share documents on a white board, share your screen or record meetings. It is available as hosted service or you download and install a package on your server with no limitations in usage or users.
QuteCom (formely WengoPhone) allows you to make PC to PC video and voice calls, and to integrate all your IM contacts in one place. Please note that QuteCom do not integrate yet Video Conferencing.