I have been a long time fan of whiteboard annotation apps for the iPad. I personally have used and loved Notability ($5.99), Show Me (Free), and Educreations (Free) In Notability you are creating "notes" and can add text, drawings, and voices. In the other 2 apps, you can record what you are creating into a movie. Teachers and students can also use them without recording as a digital whiteboard.
Lately, I have been using it for teachable moments. I will take a picture of the student's computer screen and then we can annotate it using the pencil tool. The student or I can draw on the picture of the screen and talk about the steps they need to solve the problem.
It was a great way to help a student find the patterns in their code!
I was also able to do a quick math lesson to find the angle needed for a hexagon.
I may start having students take pictures and then explaining their coding projects to me via drawing and recording. So many possibilities!