You know what a pain it can be to figure out flat bills when you've got three roommates, all sharing cable/internet/phone, plus other standard expenses like hydro and electricity. If someone doesn't pay their part, everybody else is screwed. It's easy to get bills jumbled up when IOU's are rampant. That's why a couple of roommates got together and decided to make a web app to solve the whole circular debt problem. The site is called Expensure, and it's kind of like BillMonk, but with more of a focus on roommates and travel buddies instead of flat out social lending. Expensure takes care of your flat expenses for you easily and efficiently. Simply create a ledger for your flat or trip, add your roommates/tripmates, then add the expenses, and Expensure works out the rest-- who owes what-- with their Circular Debt Algorithm. It also works on your mobile and all you have to do is join. It's free.