Brain Training.

According to the article, it's called "Touhokudai Gaku Mirai Kagakugijutsu Kyoudoukenkyuu Center: Kahashima Ryuuta Kyouju no Nou o Kitaeru Otono DS Training." You can call it Brain Training.

Well, you hold your Nintendo DS like a book (with left and right screens), and you basically use the touchscreen to undergo a wide variety of simple, cleanly-designed, interesting exercises intended to make you smarter. Or, at least, keep your brain sharp and fresh and delicious.

Not actually a game, but an application that tests your mental acuity and reports your "mental age." The #1 game in Japan is a non-game.