DuoCards is a vocabulary‑building app that lets users capture words from videos, articles, subtitles and courses and store them in personal decks. Users review the saved items with AI‑enhanced flashcards that incorporate spaced‑repetition, pronunciation drills and short conversational practice. The app combines classic flashcard review with an AI tutor that can generate examples, explain grammar and simulate daily‑situation dialogues. It also supports offline review and tracks progress across multiple languages.