There is a new app in the Chrome Web Store called Explain Everything. The app is described as a screencasting, interactive whiteboard, in which, if you cannot explain everything, it probally can't be done.
In this intro video I go through the basic menu options. These include drawing, shapes, grouping, zooming, inserting text, and inserting objects.
This app is designed for a touch screen and certain interactions with the touch screen may not be obvious at first. For example, initially I wondered why text size could not be increased or additional shapes were not available. A hard press on specific tools bring up additional features.
The more I played around with this app the more impressed I became. There is a slight learning curve but this allows you to work in more advanced ways within the app.