BouncyBill is a BlackBerry PlayBook application written using Adobe AIR (and a dash of the BlackBerry PlayBook SDK) that splits a bill between multiple users. It features a natural and fluent user interface (thanks in no small part to Tweener) that is still unlike anything else on the PlayBook, even after almost a year of availability on BlackBerry AppWorld.
However, it also still has some bugs because a license to Adobe's Flash Builder is prohibitively expensive. As such, I'm putting this on Github to see what people will do with it. Have fun, guys!
One suggestion: It's very easy to remove the BlackBerry dependencies, turning BouncyBill into a pure Flash app - in fact, that is how I did much of the testing during development. Maybe I'll get around to forking and creating that pure Flash version in the next few days, but if someone beats me to it, more power to you ;)
(The last release of BouncyBill can be downloaded for free from the AppWorld).