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.

iDoneThis - iDoneThis The fun, easy way to get stuff done. Every day we’ll email your team to ask, “What’d you get done today?” Just reply to our email. The next day, everyone gets an email with the team's accomplishments

Eduflow - Digital learning that actually teaches students something

Jell - Helping distributed teams thrive through async daily standups - all in minutes a day.

Kialo - Kialo is the platform for rational debate. Empowering reason through friendly and open discussions.

How to Acquire More Users - The growth guide used by Y Combinator companies