I’m sure the algorithm can play a huge role in the effectiveness of learning but for me the difficult part was always creating the cards and actually opening the app to practice.
I've built Komihåg [1] to try and combat this: Select any text on your iOS device and a flashcard is automatically created for you, and the app is then showing you the cards on the Home Screen / Lock Screen / Apple Watch Face.
I haven't gotten to implement any sophisticated scheduling algorithm yet but will definitely do that eventually.
[1] : https://komihag.com
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