The most popular spaced repetition software is Anki
It's used a lot in Medical school.
Other options are Supermemo and AnkiPro.
Memory
Spaced repetition is when you study something at increasingly large intervals over time.
Here's an example. You make a new card. On the first day, you'll maybe study that card twice. Then the next time you'll study it is in a week. After that, it's in a month. After that, it's in six months. This way, you spend less time studying each flashcard but can remember it forever.
Optimal spaced repetition shows you a card right before you're about to forget it.
Q: why?
Spaced repetition is at least 20x more time-efficient than normal studying.
