I am using CometD Java Library and HTML 5 Canvas to implement real time drawing application in my final year project. This is a very first draft version that created by me. I have tested by opening four browsers, and writing in one browser, and it can be seen that all 3 other browsers will draw itself. However, here should have other problems that I am going to fix it up. The source code is not available for this moment.
Here have a look for.