Lots of comments about using your own systems etc so I'll say two things:

1. The biggest win is just doing spaced repetition. Period

You don't even need an algorithm. You can just have options for "remind me in 1 day, 7 days, 14 days". This is how people did with physical cards: they just put the card at the back of the deck, the middle or the front.

2. LLMs now make it trivial to just say "make me an Anki clone in python with these features" and it will come up with something pretty decent.

In closing, learning the things that LLMs can't do quickly and efficiently is basically what we should all be doing.