Kanji Box
Kanji Box is a cool, little application for Facebook which allows the user to learn and/or test their Japanese skills. It’s mostly a reading application, but you are likely to pick up a few new words along the way. You need not know any kanji to use this application as there are also kana quizzes. You can change the level of kanji tested to any JLPT level or Japanese grade level you wish to quiz yourself at whatever stage you are at in your kanji studies.
For those with a competitive streak in them, you can also work on improving your personal high scores, compare your high scores with other Facebook friends, and stare in wonder at the leaderboard (which I am still 250 points away from). On the stats page, after taking a few quizzes, you can see what level you are at. For instance, I can see from my results on the stats page that I can easily pass JLPT 4, JLPT 3, and JLPT 2, but I’m borderline passing for JLPT 1.
You can even export printouts of kanji you miss for offline studying.