Sleep for Android (a popular sleep tracker/analyzer) allows you to "pay in" a small amount of money, like $5-15 per user choice via in-app purchases, that is lost as a donation to the developers if the set goal wasn't reached and refunded otherwise.
I thought that was a pretty clever way to go about it, I know people do a lot for $5!
I thought that was a pretty clever way to go about it, I know people do a lot for $5!