Stockfish.js 19 (lite, single-threaded) — https://github.com/nmrugg/stockfish.js (release v19.0.0, npm package "stockfish" 19.0.0)
Based on Stockfish — https://github.com/official-stockfish/Stockfish
Licence: GNU GPL version 3 — full text in COPYING.txt.
The files here are the unmodified release build. Complete corresponding source code:
  https://github.com/nmrugg/stockfish.js/tree/v19.0.0
  https://github.com/official-stockfish/Stockfish
The chess app around it (../../index.html) is a separate program that talks to this engine over the UCI text protocol.