You already know Luis von Ahn’s work. He helped create CAPTCHA, the technology that helps control spam on the internet and crowd-sources humans to help computers read and digitize old text. In 2012, he co-founded Duolingo, a free language learning app. To him, the app was meant to solve “this mismatch where most of the people trying to learn a language didn’t have $1,000, whereas the software that would teach you a language cost about $1,000.” Von Ahn says there are now more Americans learning on his app than there are in the public school system. Why? Because Duolingo works like a video game.