Solvr is a service that allows users to privately or publicly get help solving problems step by step. No need to create an account and the service is completely free. You can share your URL with friends or colleagues and collaborate on your problem in real time.
Once you submit your problem users can provide feedback by commenting or providing an idea. Users can also vote on a topic or idea and give it popularity. At the same time, any feedback to a problem can also be responded to create ultimate collaboration.
Teachers could use this to ask students for ideas on how to answer a word math problem, provide what if scenarios in science and social students. English teachers could provide students a poem and they could interpret its mean and then students could comment on those interpretations. Solvr reminds me of another option to a backchannel but with a specific concept.
Check it out and see what you think. Here is a short example of how a school used the service to gather ideas on an issue they were having. It can give you an idea of how the service works.