Gynzy
This is a whiteboard app.
RealtimeBoard: Whiteboard for Collaboration
This is a whiteboard with a large number of features.
Ziteboard - zooming collaboration whiteboard
This whiteboard allows you to see what is being done in "real-time." The whiteboard has a number of features.
Explain Everything
You can get the classic whiteboard called Explain Everything for Chrome, but it only works on Chrome OS.
Whiteboard Lite by Lesson Monkey
This is a very good whiteboard app.