Dropbox Paper - A collaborative document-editing service
Smoothboard Air - Smoothboard Air is a collaborative interactive whiteboard application for iPads and Android devices that revolutionizes interaction in lecture rooms.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.
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.
Ghostnote - Add notes to anything.
RealtimeBoard - RealtimeBoard is an online collaboration software created as a team collaboration and online brainstorming tool. It's super easy to use & free!