Host and Document Collaborative Brainstorming Sessions With Realtime Board - The service allows you to work with any information and visual content on one board individually or with a team. You can work with images, videos, PDF-files, write notes and comment everything, use colorful post-it stickers and files from your Google Drive. The free education version allows you to create unlimited private and public boards, have an unlimited number of collaborators, and 3GB of storage space.
The all-new My Simple Surface is just that: a very simple online whiteboard surface with no registration required. You can write, type, and even create mind maps with just a few keystrokes...you can even share your surface with up to three people. This one works on iPad, as well!