I have found 3 programmers are useful for learning Japanese on my iPhone. The first two are dictionaries based Jim Breens jmdic and KANJIDIC2. I am not sure about the third. For s straight Japanese to English Dictionary "Japanese" is what I use it also includes some JLPT level divide flash card practice. The second dictionary is Shinkanji. Its strength is it accepts handwritten input for Kanji you don't know the pronunciation of, also it good for browsing from Kanji to Kanji by radicals. Both show stroke orders and lets you keep lists.
As study tool I use my iPhone the most not with a app but a website ReadTheKanji. It is a Kanji flash card site but with two differences. First it shows you words like "行く" or "説明" to learn instead of single Kanji with all the possible pronunciations and meanings. I find it much better memorize one thing at a time than 5 things at once. ReadTheKanji reduces it 2 things, a reading and an English meaning. It also give a sentence for each word. Its layout is not good for the iPhone but I still find myself spending hours reviewing and learning new words/Kanji with it. The other frustrating point is that the site is often slow. An iPhone app version would solve both these problems. Hopefully I will be writing that app with them in the coming months. It is an app I would use a lot so I want it done right and as they say - If you want something done right do it yourself.
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