Senatus - Upvote for questions around a given topic.

Attendize Event Ticketing - Attendize is a free & open-source ticket selling and event management platform

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.

Zoho Backstage - Plan, run, and analyze your event— all from one place

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.

Meetup for iOS and Android - Discover groups that are all about the things you love