Although almost any software that uses Japanese will help you to improve your language skills, these are specifically intended for teaching Japanese. Free Light Japanese Uses multimedia presentations to teach vocabulary, writing, and procunciation.
Teachers can easily create new lessons.
Available for both Windows and Macintosh. Kanji of the Day Daily text files presenting a kanji for learning. Beginning Kanji Stacks HyperCard software from the Univ. of Minnesota for learning the kana and beginning Kanji studies.