Bigbluebutton - Open Source Web Conferencing

BigBlueButton is an open source web conferencing system for distance education. It supports sharing of slides (PDF and any document readable by OpenOffice), webcams, whiteboard, chat, voice over IP (using FreeSWITCH), and presenter's desktop. It can record and playback sessions (slides, audio, and chat), runs on Mac, Unix, and PC computers, and is supported by a community of developers that care about good design and a streamlined user experience.

The use cases for BigBlueButton are One-to-one on-line tutoring, Small group collaboration, On-line classes (25 or less)