MySQL - The world's most popular open source database
Kahoot! - Kahoot! makes it easy to create, play and share fun learning games in minutes—for any subject, in any language, on any device.
PostgreSQL - PostgreSQL is a powerful, open source object-relational database system.
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.
SQLite - SQLite Home Page
Mentimeter - a web-based polling tool for workshops, conferences & events