Free version of Slime Forest Adventure:
*optional introduction to katakana and hiragana
*get comfortable with kanji
*learn to recognized and distinguish a thousand kanji
*the adventure begins with Episodes 1-4
*start learning kanji readings with a sample sidequest
*introductory vocabulary and grammar in Supplementary Training
I've enjoyed it well enough back then, but it's up to you if you want to risk the download.