DrawPile - Drawpile is a drawing program that lets you share the canvas with other users in real time.

malmal - Draw together on a nearly infinite canvas with your friends or with strangers.

Aggie.io - Draw a picture together with your friends in real-time over the internet in your browser.

FlockMod - Flockmod is a free real time online group drawing app with all the bells and whistles.

QueekyPaint - QueekyPaint is a unique browser-based drawing tool for creating animated drawings online.

MagicalDraw - MagicalDraw is a free, no registration required drawing chat service. You can create a drawing chat room in no time.