This app is the companion to the web-based version of Skritter. The smartphone app makes outstanding use of the specific properties of the iPhone screen. Everything you need to practice writing, reading, meaning and tones of both individual characters and multi-char words is ready at hand, making processing vocabulary using the built-in spaced repetition system very convenient.
Submitting strokes with your finger goes very smooth.
The Skritter catalogue of ready-made vocabulary lists from official text books is vast. You can of course also compose your own list using the web interface. Skritter automatically provides the English meaning, pinyin with tone marks, voice pronunciation and sample sentences for any character or word under study.
Skritter has a very active and constructive user community. I've found the developers typically improve and add new features based on user feedback with every new release.
Highly recommended.