The classical Cows and Bulls game.
Bulls and Cows (also known as Cows and Bulls or Pigs and Bulls) is an old code-breaking mind or paper and pencil game for two or more players, predating the commercially marketed board game Mastermind.
Live demo: https://ab-cnb.herokuapp.com/ (⚠ Currently down, because Heroku stopped offering free hosting during the pandemic season.)
