Kana Flip (Hiragana Katakana) for iOS

Kana Flip is a learning tool similar to flash cards, but with an intelligent progress tracking system that helps you learn faster. After you "flip" to the answer, you pick if you were Right or Wrong. The program remembers which Japanese characters you have trouble with, and which you have learned well. It focuses on the problematic items, while using longer spans of time between repetitions of learned material.