When I started learning Japanese last year I came across this very useful app and have been using it ever since. The major advantage if Skritter compared to similar apps is that Skritter comes with ready-to-use vocabulary sets for the most frequently-used textbooks (e.g. Genki I and II, Tobira, Basic Kanji, Heisig etc). Thus, theres no need to first copy all words from the textbook, which means you can start learning right away. Skritter will teach learners reading and writing Japanese words. If I had to choose just two apps for learning Japanese, it would be Skritter and Anki (which works a bit like Skritter but requires you to first copy all the words from your books. Anki, however, is a bit more versatile in that it can be used for learning all kinds of things, from languages to medicine).
MartinetGra about Skritter Japanese, v2.4.0