LeitnerPlus is an authenticated learning-card application built with Next.js 16, React 19, TypeScript, Tailwind CSS, and Supabase. It lets learners create visual flashcards, organize them into learning spaces, categories, tags, and colors, and review due cards through an FSRS-based spaced-repetition workflow. The project includes server-side API routes for card persistence, private Supabase Storage images with signed URLs, review scheduling, review logs, dashboard statistics, profile preferences, avatar storage, theme support, and OAuth/email authentication. Its architecture shows a practical full-stack implementation with typed validation, reusable UI components, and database-backed learning state.