Well, this is clever! There's a nifty app called 30/30 that allows you to pay 3 different prices for it. How? All are in-app purchases, but don't really unlock anything. It's not a donation, which isn't allowed, because the developer isn't a non-profit and you are paying them for the shareware. It's just a clever way of using the App Store for an honor system.
The app itself is a timer app, used to set timers for activities. Similar to the minutes prescribed in the Pomodoro technique, except 30/30 allows a range of timing. The app is free to download, as the payment is up to you.
[via The Guardian]