Kanji Book - Learn Japanese online with kanji mnemonics. Study all of the jōyō kanji with the best spaced repetition system. It's easier and better than any flashcard app.
StudySmarter - Your lecture notes, flashcards, summaries, learning with friends, statistics, and even rewards for learning - all in one place and just a click away - StudySmarter.
StudyMD - Flashcards from Markdown. Built with electron for OSX.
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.
Avokado - Language learning app
Repetitions - Repetitions is a cross-platform spaced repetition system (SRS), an intelligent flashcard application that makes learning and memorization easy.