It is not as game-ified, but you can have a look at anki. There are plenty of premade decks about various topics to learn with.

There are a few other providers that do lifetime subscriptions. Filen.io and pCloud come to mind.

If you like open source projects, have a look at the banglejs. It can do most of what other smart watches do, but privacy friendly, and with a runtime of about a week per charge. However, it is less flashy/shiny and a bit more experimental than the Apple watch and the like.