Cards sorted based on test outcomes. Cards are classified into
five proficiency levels. Correctly answered cards are moved one level
to the right, and incorrectly answered cards are moved to the left. 
This neatly separates unknown cards from those you already know.
Efficient card selection mechanism. The matrix-style card selection screen enables you to select cards by set and by proficiency level, in any combination you choose. You have fine-grained control over which cards to include in your next review session.
Card "urgency" indicated through color-coding. Cards are color-coded on a spectrum from green to black based on their test history to indicate how urgently they are in need of review. You always have detailed information about the state of your flashcard deck at your fingertips.
Free Jōyō Kanji deck. A free Jōyō Kanji deck covering all 2,136 characters is included with the app. The app also contains 
free Hiragana and Katakana decks.
Supports 4-sided cards. The app supports flashcards with up to four sides. When studying Kanji, you can separately uncover the Kanji character, the kun'yomi reading, the on'yomi reading, and the English keyword.
Supports importing your own flashcards. The app supports importing your own flashcard decks in *.csv and *.xlsx format. Using this functionality requires an in-app purchase.
Export flashcard decks to files. Save your flashcard decks to external files that store cards contents, proficiency state, learn history and deck settings. Make backup copies to protect your flashcard data, transfer your decks to other devices or share them with other users.
Over 50 vocabulary decks available. Interested in Food? Animals? 
Movies? Politics? Law? Computers? Furniture? Mathematics? Sports? Vocabulary decks for more than 50 subject matter areas are available as in-app purchases.
No registration required. Mindframes does not run a back-end server and does not require any registration or login. In-app purchases are processed by Google Play through your Google account.
Works offline. Other than to complete an in-app purchase, no internet connection is required to use the app, so you can practice your cards on the subway, on an airplane, or wherever you go.
Use spaced repetition. The card selection screen makes it easy
for you to select for repetition precisely those cards that you find
most difficult to remember, and skip the ones you already know. 
By
repeatedly selecting cards in lower proficiency levels on the left side
of the screen, cards that you have already mastered will gradually get
excluded from your review sessions, and cards that are difficult for you
will show up with ever-increasing frequency.
No automatic scheduling. Unlike other flashcard apps, there is no algorithm that tries to decide for you which cards you should review. A card scheduling algorithm that is flawed will lead you to spend too much time on cards you already know (and too little on the cards you really need to focus on), which can impair your performance and slow down your progress. With Mindframes, the decision which cards to review is always up to you.
Customize your study. Versatile settings enable you to change
the order in which card sides are displayed, select the number of
proficiency levels by which unknown cards are demoted, 
control the order in which cards are shown during review
sessions, change the algorithm for computing card "urgency", and edit
card contents.
If you would like to use Mindframes to study a subject other than Japanese, consider using the "classic" version of the app, which is called "Mindframes Flashcards" and can be purchased here. This is a plain-vanilla version of the app which allows you to import your own flashcards in *.xlsx, *.csv and *.txt format, but does not include a preloaded collection of Japanese flashcard decks or an in-app purchase mechanism.
If you have questions about Mindframes Flashcards: Japanese, please take a look at the Help & FAQ. There is also a separate FAQ for Mindframes Flashcards, 
which is available here.
To learn how your personal information is handled while you use Mindframes Flashcards, please read the Privacy Notices. The Privacy Notice for Mindframes Flashcards: Japanese is available here, and the Privacy Notice for Mindframes Flashcards is available here.
The End-User License Agreement for Mindframes Flashcards: Japanese is available here, and the End-User License Agreement for Mindframes Flashcards is available here.