Ziteboard - Ziteboard is an zoomable online whiteboard that lets team to collaborate in real-time.
Slack - A messaging app for teams who see through the Earth!
Witeboard - A real-time whiteboard for your team. No signups required.
Smoothboard Air - Smoothboard Air is a collaborative interactive whiteboard application for iPads and Android devices that revolutionizes interaction in lecture rooms.
Smart Kapp Whiteboard - Connected whiteboard that saves notes to your app
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.