Duolingo

Duolingo is the most downloaded education app globally, with 100+ million monthly active users learning 40+ languages through gamified lessons. Its free tier includes all languages with ads, and studies show it matches university courses in reading and listening comprehension. At $7/month for Super Duolingo, it is 50% cheaper than the typical language subscription service. While #6 MIT OpenCourseWare offers deep academic content, Duolingo's streak notifications and leaderboards exploit addictive psychology to keep you learning Spanish. It went public in 2021 with a $6.5 billion valuation, proving its cultural and educational impact.