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.
GitBook - Modern Publishing, Simply taking your books from ideas to finished, polished books.
Synonymful - Improve your vocabulary and communicate like a pro.
MkDocs - Project documentation with Markdown.
Fluent - Fluent is a people-based marketing platform that uses real-time, one-to-one interaction to create custom audiences and serve personalized ads that drive performance at scale.
Docusaurus - Easy to maintain open source documentation websites