A regular question people ask me is: How can I easily and quickly get feedback from a class or audience? Setting up a back channel for conference sessions, workshops or classes can get you the instant feedback you need to monitor learning. Your class/audience already has their own devices, “providing authentic use of edtech tools, students understand the potential their personal device(s) have on their continued development.”
TodaysMeet is the one I go to. Here is a recent article from Emerging EdTech: Using TodaysMeet as a Formative Assessment Tool.