I've seen many Japaense learning tools pop up over the past couple years that are effectively some useful tools integrated with, or a thin wrapper around, a spaced-repitition flashcard system.

There were several that seemed really useful and I would've liked to try them, but every single time I decided against it because I really don't like the idea of having my flashcards be locked to that platform. It's such a shame.
All of these would be way more appealing if they just integrated with Anki.