I included this app in my Christmas Day post 11 Awesome Apps to Try on Your New Android Device, but I think that it deserves a stand alone post of its own.
Sync SpaceÂ is a whiteboard app available for Android devices and iOS devices. You can use Sync Space to create drawings and documents on your tablet. You can create using free-hand drawing tools, using typing tools, or a combination of the two tool sets. Your drawings and documents can be sent to and synced with other users so that they can comment and edit your drawings and documents. If you have installed an app like Evernote or Dropbox you can upload your drawings to either of those accounts too. Learn more about Sync Space in the video below.