You can find it here https://github.com/DataArt/chip-in-calculator
http://chip-in.me - live
Chip in calculator
When you buy something collectively, you might have a situation when some of people chipped in the purchase and some don't. Moreover people who has contributed might had non-equal contributions. It there are more that 5 contributions it becomes a pain. The app allows you to calculate how much and who should return the money within the group in that case.
It's made with polymer-project.org.