I had used Anki for a few years but recently migrated all my cards out of it and into a custom app I built just a few months ago. It is as an Elixir/Phoenix app with a simple UI but also with a rich API for Agent integration.

I use both actually. Anki for the reviews since the spaced repetition is hard to beat, but I use Norsha Notes (norshanotes.com) to generate the cards. You upload your notes or study material and it creates flashcards from them using AI, then you can export as .apkg and import straight into Anki. Saves a ton of time over making cards manually.