Duolingo

Duolingo is a language learning application built around short, frequent practice sessions. A lesson is a few minutes of exercises: translate a sentence, match a word to an image, or complete a phrase by tapping word tiles. Progress is measured in a streak of consecutive days rather than in completed units. The design choices are deliberate. Lessons are short enough to fit into a gap in the day, the streak creates an incentive to return, and the difficulty curve is gentle enough that a beginner is not blocked early. A spaced-repetition system decides which vocabulary to revisit, and mistakes are reintroduced rather than dropped. The limitation is depth. The platform builds vocabulary and recognition well but does not, on its own, produce conversational fluency: there is no live conversation partner and limited open-ended production. Learners aiming at fluency typically combine it with speaking practice elsewhere.