Deep Font Challenge is a little arcade shooter which displays one character in two or more fonts, and tells you to "shoot" the one that's in a font named on the same screen. If you choose wrong, you lose one of three lives, and if you choose right, you score points. At game end, you can post your score to a shared leaderboard.
That's it, really; a very simple system. What's interesting is that it uses the pre-existing knowledge base of its players. Many non-digital games and puzzles do this -- trivia games, crosswords -- but it's a dynamic that's quite rare in digital games.
It probably won't hold you for more than a few moments, unless you are a serious type geek, but it's well executed for what it is, and you might even learn a little typography.
Fonts!
Haha, that's awesome! This may spur me to really start studying typography in a serious manner instead of the dabbling I've done so far.
One wonders, though, how many people can really differentiate fonts based on a lowercase o. Hm.