What makes a great online whiteboard?

• Unlimited canvas:
  A digital board should mean that you're no longer limited in how big or complex your visualizations are.
  

• Collaboration features:
  Allow easy collaboration (real-time preferred) and comments by users.
  

• Ability to attach files:
  The ability to attach links, images, and other files to your whiteboard for easy reference
  

• Access from anywhere:
  Web-based platform allows students access from any device, no login required.