Japanese Resources
Hiragana to Katakana User Script
A browser user script that converts hiragana on every site you visit to katakana. Great if you want to get more practice reading katakana.
Warning: I recommend not using this until you can read hiragana effortlessly and know very well the situations in which each script would be used.
Numbers Listening Practice
A very simple web app that will read numbers to you and you have to then type them in.
Japanese Weekday Tray
A simple desktop application that shows the kanji for the current day of the week as a system tray icon.
Written in Python; requires PySide. Currently there is no convenient installer/package; you have to manually set it up.
(Yes, I am aware 14-09-2013 was not a Friday; I was simply using 金 for the screenshot because it looks the fanciest)