Dimdim is an open source web meeting product with features like Application, Desktop and Presentation sharing with A/V streaming and chat. No attendee installation - all features are available through a web browser. Dimdim can be integrated with Moodle.

Main features:
-Schedule a Meeting
-Start a Scheduled Meeting
-Record your Meetings
-Share your Whiteboard
-Share an Application
-Share Polls
-Share your Documents
-Share your Desktop
-Share a Region
-Share Widgets
-Share Mashup

Source code:
http://sourceforge.net/projects/dimdim/