The app uses my JS3 drawing and animation library and multi-user communication is handled via Socket.IO.
It gets a little crazy when more than a few people are connected as everyone tends to draw over each other but that notwithstanding it works quite well.
My intention was to eventually assign each user to their own "layer" so that they could be toggled on and off or manipulated as layers are in Photoshop.
As a personal project it gave me a good opportunity have some fun and to showcase JS3 and get more acquainted with Socket.IO.