lila

Lichess.org is a fully open-source, ad-free online chess server designed for real-time gameplay and accessibility. It provides features including game search, computer analysis powered by Stockfish via the Fishnet cluster, tournaments, simultaneous exhibitions (simuls), forums, team play, tactical puzzles, mobile apps, and collaborative study boards. The interface supports over 140 languages through community translation on Crowdin. Technically, Lichess uses Scala 3 with Play Framework, Pekko streams, and MongoDB for storage, indexed by Elasticsearch. WebSocket handling is delegated to a separate service using Redis. The frontend is built with TypeScript and Snabbdom, styled with Sass. All rated games are published as a free PGN database. Browser compatibility includes modern versions of Firefox, Chrome, Edge, Opera, and Safari. The project encourages contributions via GitHub issues and Discord, and offers a competence development program for contributors. Licensed under AGPLv3+, Lichess maintains transparency with public architecture diagrams and source repositories.