"Human Japanese" is sort of a funny name (as opposed to "dog Japanese?"), but it's a great piece of software if you are interested in learning or reviewing the basics of Japanese. Back in the early 90's when I was actively learning Japanese and also playing around with HyperCard on the Mac, I tried to develop some interactive Japanese lessons for vocabulary and for learning to read and write hiragana and katakana. I didn't get very far - it's a lot of work for one person and there wasn't much system support for this sort of thing in HyperCard.
But "Human Japanese" (version 2.0) is just the sort of thing I had in mind - self-paced, interactive, friendly, and easy to use, and best of all, it now runs on the iPod Touch (and iPhone) with its amazing touch-screen interface and audio capabilities (used for ~1800 native Japanese speech samples). The program covers basic grammar and vocabulary as well as reading and writing the two phonetic syllabaries, hiragana and katakana.
I played with the free "lite" version for about 10 minutes before deciding to spend $10 on the full version, which is an amazing price for any introductory Japanese text book, let alone an interactive one with embedded audio and animations. Learning Japanese is an interesting and complex task, and I still have a lot of interest in Japanese learning methods and materials, as well as an affection for the language. I would like to retain some level of skill even though I rarely go to Japan these days (my most frequent Japanese task is checking business card translation proofs for colleagues at work who are traveling to Japan).
Based on the quizes I have tried in several chapters, I still know this basic material pretty well, but anything that gives me a reason to play with Japanese is cool, and I really like this app a lot. It's 30 MB with 40 chapters, with many exercises and quizzes, audio for all Japanese text, and a lot of explanatory English text that is actually fun to read. It quickly transitions you to reading and writing Japanese in the Japanese phonetic system rather than in "Roman letters" which is a really useful thing (for further study as well as for reading many signs and menus in Japan).
If you have an interest in Japanese study at any level, I think you would like this learning software. You could learn basic vocabulary and grammar as well how to read and write kana very quickly and easily, and it would also be good for reviewing the basics if you're a bit rusty. It's available now for Windows XP or Vista in addition to the iPhone/iPod Touch version. A browser-based version is planned for Mac/Linux users.