This is the world’s most popular language-learning app and for good reason. More Americans are learning languages on their phones with Duolingo than in the entire US public school system. I’ve used it for multiple languages, and I’m now using it 20 minutes a day for Korean. This has been the easiest to stick with, now that I’m back in the US and running around. I’m also one of their early investors, so I might seem biased, but I canvassed everything in the language-learning world at the time, and Duolingo was my sole bet, as the approach made perfect sense to me, and their beta testers were rabid fans. More than three million people have used Duolingo every day (365 days unbroken) in the last year.