Dimdim is a free web conferencing service where you can share your desktop, show slides, collaborate, chat, talk and broadcast via webcam with absolutely no download required for attendees.
You can host or attend web meetings complete with audio and video conferencing as well as screen and application sharing. Open-source is an emerging technology in the webinar world and once it establishes itself may become a serious contender to the commercial vendors.
Register at their Website http://www.dimdim.com