Aggie.io - Draw a picture together with your friends in real-time over the internet in your browser.
PaintBerri - PaintBerri is a free art site that offers an awesome oekaki community.
FlockMod - Flockmod is a free real time online group drawing app with all the bells and whistles.
Brush Ninja - Hand-drawn Animated Gif Creator
DrawPile - Drawpile is a drawing program that lets you share the canvas with other users in real time.
okekai - A small community site where you can draw, animate, and chat through pictures all for free