Just like the Korean one, this is a very strong application for building your vocabulary. 2000 words structured in very coherent and very nice categories. Excellent way to learn, and retain japanese vocabulary.
Pros: Flashcards are very useful. Tons of useful, everyday words. Great way to learn and keep learning on the go. Great for reference as well.
Cons: Sound is a bit soft, but still bearable.
All in all, a really great application.
Longhorns9012 about Learn Japanese - WordPower