Duolingo

Duolingo /ˌdjuːɵˈlɪŋɡoʊ/ is a free language-learning platform that includes a language-learning website and app along with a crowdsourced text translation platform and a language proficiency assessment center. Duolingo is ad-free and offers all its language courses free of charge. The language-learning website and app offer over 50 different language courses across 23 languages; more than 30 additional courses are in development. The app is available on iOS, Android and Windows 8 and 10 platforms with over 100 million registered users across the world.

https://en.wikipedia.org/wiki/Duolingo