Muddiest point (see video above) has always been the classroom assessment technique (CAT) I've used most, in teacher training more than in language teaching.
When the excellent Classroom Assessment Techniques: A Handbook for College Teachers [Amazon] first came out in 1988, authors Angelo and Cross envisaged teachers collecting information from the learners on slips of paper or card. I've stopped doing it that way as I've found that it works great with an Edmodo group.
There are many ways you can use CATs. If you want the answers you collect to be anonymous, Edmodo isn't going to work for you; if you want to keep the answers "secret" in some way, it's not your tool either. Personally, I prefer to sacrifice anonymity, make it optional, share the answers with everyone in the group and have the learners help clarify the muddiest points mentioned in the replies to the group.
The Angelo and Cross manual is a book all teachers should read.