Kanabox is a simple and straightforward js I wrote when I was learning Japanese. It turns the text input into a kana input by transliterating the input. Just type UPPER for Katakana and lower for Hiragama: "KANA" -> "カナ", "kana" -> "かな" and double n (nn or NN) for "ん or ン".
Just type "ohayougozaimasu" to get "おはようございます"