This app was mentioned in 2 comments, with an average of 1.00 upvote
skritter...the monthly cost ended up being more than i was willing to pay, but if it had been a one-time purchase i would definitely still be using it daily.
the best feature is that it gives you stroke-by-stroke feedback when you are writing a kanji...other apps like obenkyou will let you write an entire kanji and then mark it wrong because you did one thing out of order, or in the wrong direction, or not starting in EXACTLY the right spot, but skritter will not allow you to go on to the next stroke until you get the current one right.