Duolingo
Free tierLearn a language for free — powered by AI and gamification
Free tier available·All audiences·Powered by OpenAI (GPT-4)
Key strengths
Gamified learning with streaks, XP, and leaderboardsAI-powered personalized lesson paths40+ languages supportedBite-sized lessons optimized for habit formationGPT-4-powered Roleplay and Explain My Answer features (Max tier)
Free tier + paid plans · from $6.99 USD/mo
Pittsburgh, USA
Founded 2011
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- AI conversation simulation (Max) — Integrate GPT-4-powered Roleplay scenarios to give learners dynamic, unscripted speaking practice beyond fixed dialogue trees.
- Spaced repetition research — Duolingo's publicly documented SRS and IRT models serve as reference implementations for EdTech developers building adaptive learning systems.
- Large-scale A/B experimentation — Duolingo's experimentation framework (used internally) is a case study for ML-driven product optimization at scale.
- Duolingo for Schools API (limited) — Educators can sync class rosters via Google Classroom integration and track per-student XP and lesson completion.
- Duolingo English Test (DET) — An AI-proctored, at-home English proficiency test recognized by 5,000+ institutions; results delivered within 48 hours via ML scoring models.
- Mobile SDK / offline ML — The app's offline lesson delivery and on-device speech recognition for pronunciation exercises represent a mobile-first ML deployment model.