I am interested in making a realtime collaborative drawing system similar to http://flockdraw.com/ . However I would like to only use open source tools (flockdraw uses flash and also limits the number of users) and also I will host it myself.
I have been considering writing the whole thing in Java. However I realize I am not up to date with recent advances in programming languages/libraries. What would be a good programming language/library combination to do this task?
Update. This question/answer looks very relevant.
See:
The basic principles for this is generally pretty easy. Just communicate the shape that has been drawn to the other users - as you suggest. With that in mind there are a number of open source realtime web technologies that you could use.
I've seen apps like that using HTML5.
Take a look at this app. I think it can help you get started.
This kind of apps usually take advantage of HTML5 Canvas and probably HTML5 WebSockets. There are lots of libraries and tutorials out there.