L-Box.

L-Box is an implementation of the Leitner System, a spaced repition device designed in the 1970s by Sebastian Leitner.

You start by creating a deck of flashcards.

These flashcards are sorted by proficiency level. Every flashcard starts at level 1. Each time you quiz yourself, you test your knowledge of cards grouped of proficiency levels. Every day you study level 1, every other day you study level 2, every third day you study level 3, and so forth.

If you guess a card correctly, it moves up one proficiency level. If you guess it wrong, it goes back down to level 1. Once you correctly guess a card that's in the 7th level it's archived.

And that's it!

If you want to learn more about this technique I recommend checking out

Try it out!