Check out www.warpaint.se. The guys there have been working on a server client for an ol' classic that I just discovered called OpenCanvas 1.1. Although it doesn't have many features as a drawing/paint program, what it does do is pretty great. It's like the Wings3D of 2D. But in addition to being quite responsive to stylus input, it also features two other great abilities which are networked drawing and event recording. Networked drawing means that you can paint in realtime with up to 3 other users on the same common canvas. The event recorder is pretty neat, because it replays the whole drawing process. So you can download from other people to see how they went about drawing something, or you can save your drawing to an event file and show others what you did. Not bad for a free program... Oh yeah I almost forgot, the WarPaint Server client. Duh! Anyhow it's a little proggie written in Java that allows others to see your networked session online via the WarPaint website so others can join. It also features more advanced controls over a drawing session so you can boot troublemakers, have new people resume from when a session started, etc. Pretty neat stuff that goes one step beyond what OpenCanvas 1.1 does in networked mode.
Check out the vid of some OpenCanvas 1.1 drawing in action.