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Level Up Lingo is a website, currently in beta, that's designed to quiz you on JLPT vocabulary words.
Once you've picked the level you'd like to review, you're taken to a page with a simple background image (that you can change, along with the text color, via the options at the bottom of the page). In a pixelated font, words appear on the screen in Japanese. You then use the arrow keys to choose the answer. If you are correct, the answer is highlighted in green. If you are incorrect, the meaning you selected will be highlighted in red, and the correct answer will be highlighted in green. When you're ready to move on, you just hit enter.
It's a strangely satisfying way to quickly review words when you have free time.