DrawPile - Drawpile is a drawing program that lets you share the canvas with other users in real time.
Aggie.io - Draw a picture together with your friends in real-time over the internet in your browser.
Formgraph - Formgraph is a collaborative vector drawing tool and social network.
Panel Jam - Collaborate with others on comic strips
QueekyPaint - QueekyPaint is a unique browser-based drawing tool for creating animated drawings online.
Drawception - The browser-based party game that combines the telephone game with drawing! Hilarity ensues.