BigBlueButton is an open-source web conferencing system targeted at the higher education market, specifically for use in distance learning. It provides a good set of general conferencing features, as well as semi-participatory presentation plus whiteboarding functionality.

Good Features

• "Moderator" role for one or more participants
• One participant at a time has "presenter" status (assigned by a moderator)
• Import presentations from a file (PDF or PowerPoint)
• "Presenters" can page through presentations; all participants will see the same slide
• Whiteboard overlay with pen, rectangle, and circle tools
• Whiteboard contents are distinct per-slide
• Record and subsequent playback of presentation including slide content and timing, audio, chat
• Polling module available
• Users can independently rearrange the application's sub-windows; a "reset layout" button is provided
• User interface runs in a web browser with low latency (using Flash)
• No assumptions regarding aspect ratio of slides
• Text chat (public channel and between individual users)
• Audio conferencing
  • Users can mute themselves
  • "Moderators" can mute other users and lock the muted state
• Any user can share their webcam and/or desktop

Missing Features

• Limited collaborative whiteboard ability because there is one "presenter"
• No layers in whiteboarding functionality
• No flexibility in lecture formats

Other Features

• "Presenter's" pointer position over the slide is shared
• Integration with CMS (Moodle etc.) to manage sessions

Screenshot