BigBlueButton

BigBlueButton is a Web conferencing system that focuses on usability, modularity, and clean design, both for the user and developer. It implements real-time sharing of voice, Web cams, desktops, slides, and chat messages to provide remote students with a high-quality learning experience. Unlike other conferencing systems, the desktop sharing works on Mac OS X, Unix, and PC computers, and there is no hard-coded limit on the number of simultaneous Web cams.