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.
The Taridium ipbx is a complete software-based VoIP PBX system that replaces a traditional proprietary hardware PBX. It runs on Linux without the need for extra software licenses, and is based on the SIP standard. It supports many phones and is available for free in a 5 user version.