If anyone's studying Japanese, I made two iOS apps for spaced repetition systems specializing in the unique needs of learning Japanese.
The first is a flashcard application called Manabi. It uses a similar algorithm as Anki with a priority on UX.
The other is Manabi Reader, which complements the flashcard app. It curates feeds of interesting short-form content, has one-tap dictionary lookups, optional furigana injection and JLPT level tagging, and it lets you create flashcards from the words you're learning as you read.
Glad to hear any feedback. I'm currently working on word tracking functionality for Manabi Reader, to track your reading progress and let you see which and how many words in an article you should know already vs. words new to you.