ReplayChess

ReplayChess is a free, open-source alternative to Chess.com and Lichess for people who want to play chess history rather than browse it. Where other sites give you a game database or a video, ReplayChess starts you at the critical position of a famous game and lets you play it out — against a friend, a matched opponent, or Stockfish in your browser.

• 50+ chess legends with playable famous positions
• 3,600+ ECO-coded openings, each playable from the position
• Real-time multiplayer with ELO matchmaking and private challenge links
• Post-game analysis: match rate vs the original moves, divergence detection, practice mode vs Stockfish
• Installs as a PWA; MIT-licensed source on GitHub

Free to play; Player plan $4.99/month unlocks the full catalogue.