At the Cocoon GetTogether 2003 the attendants were using a whiteboard system (SubEthaEdit for Mac) to collaboratively take notes of the talks.
Bertrand suggested one more (Coccinella) on the Cocoon Developers Mailinglist for doing a virtual Hackathon on the first Friday every month (which BTW is an excellent idea suggested by David Crossley).
This made me have a closer look at these tools and provide a short list of OpenSource software I found.
* SubEthaEdit (Mac, with screenshots)
* The Coccinella (Java, also Client/Server using a Jabber Server, with screenshots)
* Privaria (Windows, soon Linux, with screenshots)
* Babylon Chat (Java, client and server with Demo)
* Drawboard (Java, client and server with screenshots)
* Tulka Whiteboard (Java, client and server with screenshots)
* CodeApplet (Java, client and server with SICS Demo)
* Volley (MacOS X, client and server)