Duolingo - Duolingo is a free language learning app for iOS, Windows and Android devices. The app makes learning a new language fun by breaking learning into small lessons where you can earn points and move up through the levels. Read more about Duolingo.

vym - VYM (View Your Mind) is a tool to generate and manipulate maps which show your thoughts.

Eduflow - Digital learning that actually teaches students something

Linked Ideas - A macOS/iOS apps to treat ideas as links of concepts.

Backchannel Chat - Backchannel Chat is best in class discussion tool that is intended for teachers to streamline their class activities.

Freeplane - Freeplane is a powerful and free software for building mind maps.