Lila is the backend codebase powering Lichess, a free, open-source online chess server with millions of users. The architecture handles real-time games, puzzles, tournaments, correspondence chess, streaming, and user profiles, scaling to thousands of simultaneous matches. The system uses functional programming principles (in Scala) to maintain reliability—state transitions, clock management, game rules, and move validation are deterministic, reducing synchronization errors. Lila also...