I used to live with 3 roommates and we kept a spreadsheet in google docs of who paid for what (bills, shared groceries, etc.) The spreadsheet automatically figu

I used to live with 3 roommates and we kept a spreadsheet in google docs of who paid for what (bills, shared groceries, etc.) The spreadsheet automatically figured out who owed who and how much. Every now and then someone would pass out some cash to catch up (and log it in the sheet). It worked surprisingly well for us. I think the reasons it worked were 1) everyone agreed in principle, and 2) not entering your updates was effectively the same as giving everyone else money.