I lived in a house with three male roommates for two years while I was in college. The first year I used Excell to keep track of each bill paid, and who it was paid by, with a little formula to figure each person's total amount paid, total amount owed, and whether or not they were paying or owing each roommate. Twice a semester I would print it out and tape a copy to everyone's door so we could settle up. It worked like a charm until the boys stopped reporting to me which bills they were paying (the "we're all friends here, why police each other like this?" trap. Also known as "OMG the girl roommate has a lower tolerance for clutter and will clean up after us" fallacy). I think I was the only one who was repayed properly that semester, which, of course means I profited!