Simple Poll - The easiest way to create polls in Slack
Kahoot! - Kahoot! makes it easy to create, play and share fun learning games in minutes—for any subject, in any language, on any device.
GitHub Polls - Polls for GitHub issues and readme
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.
Curious Polls - Answer a question once a day for the chance to win £100/$100
Mentimeter - a web-based polling tool for workshops, conferences & events