This is a "progressive webapp", you can play it in the browser, or install it like a "proper" app on your mobile (Chrome/Android trhee-button-menu, "Install app"; other borwsers/platforms, please let me know!). It will keep your game stored even during reboots.
I would kill to just have a simple app to play dominoes on my phone with no ads and no BS. I almost found one. It didn't have ads between games, but it did have a stupid micro transaction scheme or online play or something. Grumble. Grumble.
This might just drive me to start developing apps. I can probably do the basic stuff but I don't know where to begin programming the cpu opponent...