Nuku is a personal Japanese tutor, teaching you the two native Japanese writing systems, hiragana and katakana. It features both these systems, all three main romanization systems and methods of selecting what to learn. It was written to aid me in my Japanese studies.

Hiragana & Katakana
Hiragana and katakana, or collectively kana, are two of the writing systems in Japanese, the third then being kanji. Kana are much more like our alphabet than kanji is though, as there are only about 70 unique characters - there are several thousand kanji.

Kana is the first thing a Japanese learns in school, and every word can be written using them. However, normally a mix of hiragana and kanji is used. Katakana is similar to hiragana but looks different. It is used instead of the latter, when writing foreign words, or for extra emphasis.

Romanization Systems
There are several methods of romanizing Japanese - that is, turning the Japanese into roman characters. The three main ones are Hepburn, Kunreisiki and Nihonsiki.

The official system is Kunreisiki. Another, Hepburn, was designed to romanize according to pronounciation, rather than a fixed table. Nihonsiki is similar to Kunreisiki.