A while back I wrote about how we have turned to Skype to reduce telephone communication costs for long distance, as well, as conference calls. Skype is not open source, however the software is free and the costs are minimal. However, hearing some one's voice is not always enough. You need to show them something wile you talk to them at the same time, such as, a PowerPoint presentation or a spreadsheet. There are some add-ons for Skype like Convenos and Unyte. They look promising, but they are not free (Unyte is free for 1:1 communication) and not necessarily easy to install or use. Browser-based services like WebEx and GoToMeeting are interesting, but do carry a cost, usually in the form of a subscription fee and require both a computer and a phone, although I guess you could use Skype as your phone.
A new open source application that simplifies web meetings and is free to use is Dimdim. It supports desktop and application sharing via a web browser. The presenter can send a video stream of himself and all of the participants can either speak via their microphone or headset. There is also a text chat option. As long as the attendee has Firefox 1.5+ or Internet Explorer 6+ and Flash 8 or greater plugin nothing needs to be downloaded. Attendees can be invited from within Dimdim and they just click the link in the email message to be transferred to the online meeting. Attendees can be running Windows, Mac or Linux. At the moment the presenters must be running Windows 2000, XP or Vista. There is a small browser plug-in for presenters to download which weighs in around a megabyte in size.
I installed Dimdim on our web server. It is a self-contained Java Tomcat/Apache application. Once I had Java Runtime Environment 1.5.0 installed, setup was rather painless with root SSH access. There is also a Windows version that you run from your desktop or Windows 2003 server.
The program is still in alpha development, but very functional. We did some informal testing at the Association. With six people connected, Firefox stopped responding and I had to restart the dimdim server. I am not sure if the fault was with the Logitech camera, browser or server. I later tried IE 7 and it seemed to work better, but I did not have more than 4 people at any one time in my second round of testing. Audio and video quality were pretty good, as were the display rates for the applications. It can work behind firewalls if port 80 is open, which is the common port for web browsing.
Dimdim looks very promising and you should keep your eye on it. Besides presentations, it could work very well for training. I do not know how well it scales, meaning how many can connect at one time for a given amount of memory, bandwidth and CPU resources. The program is still being developed, but if I was working at WebEx I would be concerned.