https://www.idorecall.com/

This was mentioned to me by Nate Maertens in our lunch discussion of edtech tools, spaced repetition, and Barbara Oakley from 2022-02-11.

Nice layout and bullet pointed reasons for using it on a slick website, but it looks awfully expensive in comparison to Anki and Mnemosyne (free). Looks like they've got pre-existing content, but a quick scan doesn't center the value of creating your own cards.