Duolingo

Since launching in 2011, Duolingo—the app that teaches users how to speak everything from Swahili to High Valyrian—has been downloaded more than 500 million times. Last year, with so many kids stuck at home, it accelerated the release of an app that gamifies learning to read and write for children ages 3 to 7. It also saw a 2,000% uptick in the use of its online English-proficiency test, allowing more international students to apply to U.S. colleges that have traditionally required an in-person exam.

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