I am looking for a good app that enables students to chat with one another in order to work on mathematics problems. The idea is that, in the old days, students would work over the phone to solve math problems; these days, they are more inclined to chat using apps. I would like to provide students with that option so that they can work collaboratively in their own voice (so to speak).
To this end:
What are the best apps for students to discuss math problems?