Senatus - Upvote for questions around a given topic.
Sli.do - Slido is the ultimate Q&A and polling platform for live and virtual meetings and events. It offers interactive Q&A, live polls and insights about your audience.
Poll Everywhere - Audience response system that uses mobile phones, twitter, and the web. Responses are displayed in real-time on gorgeous charts in PowerPoint, Keynote, or web browser.
LiveQ - LiveQ is an interactive presentation software that lets audience can ask & vote questions anonymously. You can collect the best questions that you should answer. Loved by teachers, speakers, event owners.
Glisser - Glisser makes presentations interactive – it takes regular PowerPoint, Keynote or PDF slide decks and pushes them out live to audience mobile devices. Your audience can then interact with the presenter with via polls, Q&A, voting and much more.
Bigo Live - #1 Live Streaming App in the world