Duolingo

Duolingo is a free language-learning program. Its website and mobile apps are available to anyone with an internet connection plus a computer, tablet or smartphone. Duolingo can be used on iOS, Android, Windows 8 and 10 operating systems. Duolingo allows people to learn over 106 different language courses in 40 languages. There are over 500 million people learning a language on Duolingo.
History.
The project was started by Professor Luis von Ahn and graduate student Severin Hacker. The main development language used was Python.