Koi-Koi is a free video game for web and Windows by Otakode, published on Itch.io in 2021. It got a major update in 2023.
The game is very suitable for people who want to practice Koi-Koi before playing with physical cards, because it uses rather realistic-looking graphics with Nintendo card designs and a minimalistic interface, and it doesn’t give any hints and doesn’t automatically match cards for you.
The game uses a very common ruleset that’s very close to Nintendo’s Koi-Koi rules, except the two special Ribbons yaku and Boar-Deer-Butterflies are fixed at 5 points each, with no bonus points for extra Ribbon/Animal cards.