It supports over 40 languages and has 40M users. For context, there are more people in the United States learning languages on Duolingo than there are foreign language learners in all US high schools combined.

-Duolingo English Test (9%)

-It is built for the mobile generation: courses are bite-sized, on-demand, and fun

-The content is accessible for free

-Advertising and in-app purchases (18%)

Duolingo made $162M in 2020, growing 129% y/y, and made its revenue from three sources:

In my opinion, a few key things are driving their incredible scale:

-Subscriptions (73% of total revenue)

-Great use of data and gamification to keep people engaged