[MBCook]

Anki is the most expensive app I've ever purchased, and it was worth every cent. Buying that app let me support the developer, the iOS app, the Mac app, and his syncing service.

When compared to $0.99 games it seems expensive, but let's be realistic. It's good quality software, and on a desktop it would be worth that price. The difference is that it's 100x more convenient on iOS since it's always with me.