April 2016
Sketchpad 3.7 is a web based drawing platform that is completely free. Combined with an ability to screencast, this software can be used by students to make their thinking visible and audible. Teachers can also use it to prepare drawings for use in videos or presentations. The video below shows you how to access it and gives a (brief) introduction to using it.
(I will shortly add a post that shows it being used by students)