PrimaryPaint has been discontinued. Similar sites and apps include Groupboard, which has a free version. Other options are iDroo, drawonthe.net and CoSketch. In total there are four Whiteboards like PrimaryPaint for Android, iPhone and iPad.
Groupboard is a free collaborative whiteboard (drawing board), allowing you to draw and chat in real time with other people anywhere on the internet, even with users using a web browser or an iPhone/iPad. Use it for online tutoring, collaborative design, or just for fun!
United States
iDroo is a browser-based online whiteboard and teaching platform for tutors, teachers, students and teams. It runs in a web browser without a desktop installation.
Estonia
EU
Draw on the . net is an online, multi-user, drawing website. You can also use it to draw on web pages. It is quick and easy to use.
The easiest way to draw together with your friends on-line.
CoSketch is a multi-user online whiteboard designed to give you the ability to quickly visualize and share your ideas as images.
DenmarkEU
