Each character is taught by showing you the stroke order in an animation, which then fades. You trace the strokes and a little robot pops up to tell you whether you passed or failed. As you progress, the faded character eventually disappears, forcing you to remember it on your own. If you make a mistake, you can erase your strokes.
You can listen to audio of each character and if you're having trouble remembering what a character looks like, you can ask for a hint or skip it until later.
I was curious to see how accurate the robot analysis was, so I got a little loose with things. The app does not let you pass with just anything.
It even stopped me from passing お a few times because my last stroke was going below where it wanted. I was pleasantly surprised by the strictness of my robo-friend!
The vowels of both hiragana and katakana are free, so you can download the app and see if you like it before dropping three dollars on what is, essentially, a drawing tool replacement for a teacher.
RoboKana is different from most of the "learn kana" apps out there though. Others mostly focus on multiple choice or basic flashcards.