Anki - Anki is a program which makes remembering things easy. Because it's a lot more efficient than traditional study methods, you can either greatly decrease your time spent studying, or greatly increase the amount you learn.

Machine Learning Flashcards - 300 digital flashcards

Quizlet - Quizlet allows you to review and create flashcards for a variety of subjects, such as math and reading.

Fresh Cards - Flashcards that just work

Memrise - Learn a new language with games, humorous chatbots and over 30,000 native speaker videos.

Flashcards.io - Free offline first flashcards maker