Duolingo has achieved a significant download milestone today; after a little over four years in the Play Store, Duilingo has reached the 100-500 million download bracket. There are apps in the Play Store with billions of downloads, sure, but they're mostly things that come pre-installed on phones. It's a real accomplishment for an education app like Duilingo to hit 100 million downloads.
Duolingo, for anyone not familiar, is a language learning app with support for more than a dozen languages. Lessons are split up into bite-sized chunks, so they're easy to do on your phone. The nature of the lessons varies a bit from one language to the next, but they'll all at least have written content. Some also let you speak out loud to test your pronunciation.
Duolingo is completely free in the Play Store if you want to add to that 100 million tally. Well, there are some optional in-app purchases that pump up your personal stats and streak record, not that any of that matters.