Globetrotter XL is a geography quiz game, which may sound dull, but is actually quite engaging.
The play area is a map of the word -- initially, with borders in place. Your mouse pointer is a crosshairs, and the game names a city (e.g., Bologna, Italy). You've got a few seconds to locate and click on it. You are scored by how close you get, with a bonus for doing it quickly.
This is pretty easy for say, Tel Aviv, because Israel is a postage stamp of a nation, so you're bound to be close -- somewhat more difficult for larger countries (e.g., I'm pretty clear on where Beijing and Shang-hai are, but other cities in China...). And where is Reunion exactly? Indian Ocean somewhere, but do you remember?
At the harder levels, the borders go away, which makes things even tougher.
Oh, and when you click, a green flag appears on the map at the correct location, and a red flag where you clicked, so you can also learn some geography this way.
Shared online leaderboard, nice music, and that's it; a nice, clean implementation of a simple idea with some educational merit.
(Via Kim Pallister.)