https://kaizena.com/: Google Chrome add-on (free). Both students and teachers need to have it. (It only works on a desktop/laptop).
It allows you to edit text, add text and voice comments.
You can also create rubrics.
It also allows you to create a lesson bank, and insert them as a comment.
http://blog.kaizena.com/post/170016427695/all-kaizena-features-now-available-inside-google
Tutorials on how to use Kaizena (Spanish)
My colour codes: