Credits & licenses

• Stockfish chess engine (Stockfish.js 10 by Nathan Rugg, WebAssembly build). GPLv3. Source: github.com/nmrugg/stockfish.js, stockfishchess.org. The engine runs unmodified in your browser from /vendor/stockfish.js.
• chess.js (rules and move generation), BSD 2-Clause, Jeff Hlywa.
• PeerJS (play-a-friend connections), MIT.
• Puzzles from the Lichess open puzzle database, CC0. Thank you, Lichess.
• Pieces: "Classic" (cburnett) by Colin M.L. Burnett, CC BY-SA 3.0; "Maestro" by sadsnake1, CC BY-SA 4.0. Via the Lichess project.