Matching pairs, with one difference: the pairs here mean something. Instead of turning over two identical pictures, you are joining the two halves of a fact, and every match you make comes with a line explaining it.
European Capitals is the set at present — eight countries against their capital cities, from France and Paris through to Poland and Warsaw, each with a note on why that particular city holds the title. It works as a game and as revision, which is largely the point.
The board is a 4x4 grid of sixteen cards, plays through in a couple of minutes, and remembers your best time so you have something to beat.