*** THIS PROJECT IS DEAD ***
But try http://drawpile.net/ instead! It's open source and has got an awful lot further.
CjopazeDraw is a real-time Internet collaborative drawing tool in the vein of openCanvas, pchat, or flockdraw, but designed with full cross-platform thick-client graphics tablet support, fast synchronising, and per-user undo and redo.
- Real-time network-collaborative drawing