I've used TodaysMeet. For many reasons.
Mostly to talk to others in the room during administrative district days. You know...when you are thoroughly bored (if you're my administrator, not you) and need something to do? I love TodaysMeet as back channel at great professional development when I don't understand a concept. It didn't even occur to me to use it with my students until I read Catlin Tucker's website suggestion of using TodaysMeet in the classroom.
What is TodaysMeet? If you go to TodaysMeet.com, you will be prompted to name the room and join. Whatever name you named the room will become the url for others to join ex: todaysmeet.com/1984Period3. You can also set the length of time the feed will be open AND get an archive of the conversation. Then you just have your students join and begin "tweeting" answers to whatever questions you're asking.
Yesterday my students were comparing 1984's methods of patriotism to that of our school's and the U.S.A. I would ask them to give examples of how our school promotes spirit and their responses went into a feed on everyone's device and I was projecting it on the screen. It was a nice way to change up a class discussion. It got playful too. My students began using hashtags with responses which is taking the concept of digital literacy to a completely new level.
Of course, the maturity of your students plays into what you'll do with this.