Aggie.io - Draw a picture together with your friends in real-time over the internet in your browser.
Smoothboard Air - Smoothboard Air is a collaborative interactive whiteboard application for iPads and Android devices that revolutionizes interaction in lecture rooms.
FlockMod - Flockmod is a free real time online group drawing app with all the bells and whistles.
Groupboard - Free collaborative online whiteboard, web conferencing and online tutoring software that can be embedded in your own website. Used by many online tutors, schools and universities.
DrawPile - Drawpile is a drawing program that lets you share the canvas with other users in real time.
RealtimeBoard - RealtimeBoard is an online collaboration software created as a team collaboration and online brainstorming tool. It's super easy to use & free!