Ask HN: How do you keep track of your group/shared expenses ?

We are working on a web application to help people manage and keep track of shared expenses.

1. Just wanted to get feedback on what do you guys use to keep track of such expenses ? e.g. apartment rent you split with your room mates,groceries you bought for your home, informal debts/loan

2. Is there any problem you face in the current solution you are using ?