Ziteboard - Ziteboard is an zoomable online whiteboard that lets team to collaborate in real-time.
Call to Idea - A gallery of inspiration for product designers
Witeboard - A real-time whiteboard for your team. No signups required.
AuthorBee - Organize Twitter around your interests
Smart Kapp Whiteboard - Connected whiteboard that saves notes to your app
Voynetch - Share your visual notes and graphic recordings.