The term “backchannel” refers to what teachers would call the side-conversations that happen during class. Now we know that not all of these conversations are off topic, sometimes students are getting clarification of directions, brainstorming, getting feedback, or engaging with the topic/material in some other way. Tapping into this backchannel brings all that to the attention of the group. It brings questions and answers, feedback, and other chatter that has the potential of creating a whole new level of engagement to your class. You don’t have to acknowledge everything that is posted and obviously some direction and modeling and practice using it will have to happen. You can archive these conversations and make them available for students to access later.
Todaysmeet is a free resource that allows you to create rooms that expire. (A different room for each unit? class block?) There is no signing up for you or students to use this site. Students enter a name to use and start typing. The downside is that students could put whatever name they want and you would have a hard time monitoring who is saying what (if you wanted to do that), easily dealt with by having clear expectations. The benefit of this site is that only people who have the link can join the room.
Twitter is also geared perfectly for this. The use of hashtags (#) keeps everyone together and allows for a more complicated organization to happen (if desired). This does need a (free) account for all who want to participate. The downside is the need of an account (it is free and easy to set up), and that it is public to anyone (they would have to be following a user or search for the hashtag which would limit the number of outside audience members). The benefit of this is that you could track who is saying what easier, it would be easy to access later, the conversation could continue after class ends.