Google Docs spreadsheet, one sheet per month, with shared write access. Easy to handle both recurring expenses and one-offs (hypothetical keg party, hypothetic

Google Docs spreadsheet, one sheet per month, with shared write access. Easy to handle both recurring expenses and one-offs (hypothetical keg party, hypothetically broken window from hypothetical keg party). Also easy to factor in percentage shares -- we go based on relative income because some of us make 2x what others do, but we're redistributionists like that. Only downside is that people who aren't typical hyper-fastidious programmer types may accidentally mess with the formatting or formulas without realizing it.