Collect money from roommates

The idea you and your roommates had of pooling resources and paying for rent, bills and groceries out of one account was great in theory, but hasn't worked out so well in practice. You've got a spreadsheet going of all the money that's been collected and for what, but it's a hassle to update. You need a simple mechanism for tracking, something you can label "for rent: December" or "for groceries: next week" and produce simple records.