Now I have published my first serious project, an app for learning how to write Japanese characters. It's the app I always wanted but couldn't find when I was studying. It tries to be simple to use, you just start the quiz and go with the flow. There's no need to plan and manage your studies, and it uses spaced repetition for better retention.
There's a promo page with more details up at http://www.kanjibyhand.com.
It's only for Android so far. The free version includes hiragana and katakana:
https://market.android.com/details?id=se.tokotoko.android.kanabyhand
The paid version includes (a lot of) kanji:
https://market.android.com/details?id=se.tokotoko.android.kanjibyhand
I'd be grateful for any comments or ideas for how to market this app!