NoteBookCast - A real time shared whiteboard in your browser, teach, explain, sketch. For work, study, fun.
Slack - A messaging app for teams who see through the Earth!
IDroo - A shared whiteboard for use by multiple Skype-users simultaneously. Features
Smoothboard Air - Smoothboard Air is a collaborative interactive whiteboard application for iPads and Android devices that revolutionizes interaction in lecture rooms.
Conceptboard - Instant Whiteboards for Teams & Projects
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.