Open source licences
Some of Ribbia's games run open source software. Here it is, with its licences and source code.
Stockfish (chess)
The chess computer is Stockfish 19, the lite build of Stockfish.js, released under the GNU General Public License, version 3. It runs as a separate program in your browser, and you may copy, change and share it under that licence.
Fairy-Stockfish (xiangqi and shogi)
The xiangqi and shogi computer is Fairy-Stockfish, the fairy-stockfish-nnue.wasm 1.1.12 build, released under the GNU General Public License, version 3, on the same terms.
Fonts
The xiangqi and shogi pieces use Noto Serif, and the cursive alphabet quiz uses Pinyon Script, both under the SIL Open Font License 1.1.