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.

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

gartic.io - Draw, guess, and win!

Anondraw - Draw and paint live with friends or strangers on a big canvas. There is also a gamemode and gallery.

Drawception - The browser-based party game that combines the telephone game with drawing! Hilarity ensues.