Stockfish 19.0.0 (stockfish.js build by Nathan Rugg / Chess.com), GPLv3, see COPYING.txt.
These engine files are distributed unmodified, as a separate program that RewindChess talks to over UCI in a Web Worker.
Corresponding source: https://github.com/nmrugg/stockfish.js/tree/v19.0.0
Upstream engine: https://github.com/official-stockfish/Stockfish