I really enjoyed using TodaysMeet! We experienced using it during one of our inservices and enjoyed how it allowed us to continually ask questions without interrupting or worrying about forgetting our questions.
Two other favorites of mine included Wallwisher, and Poll Everywhere. Both of these tools required simple set-up processes and could easily be integrated into any class, regardless of the subject!
Poll Everywhere would definitely be a class favorite! It appeals to the students by allowing them to do what they do best, text! On the other hand, Wallwisher allows students to post questions, comments or concerns on a virtual sticky note. It sure beats taking notes the "old-fashioned" way!
All of the resources above are absolutely perfect for encouraging discussion in and out of the classroom because it allows every student to voice their opinion in a non-threatening, non-verbal, non-intimidating atmosphere and manner!