Who owes whom?

One saturday, my 6 roommates and I decided to settle accounts. It took more than 2 hours to enter all the expenses in a spreadsheet and do the maths to know "who owes whom". During these 2 hours, we argued once again about the way we should settle accounts : a spreadsheet shared on our local network versus a simple sheet of paper with a calculator. I was for the spreadsheet : no calculations mistakes and you can add a forgotten expense without doing all the maths again. Those in favor of the paper thought the spreadsheet was too complicated. This afternoon decided me to create a small project that would just answer the question "who owes whom" without installing any software, nor managing a shared spreadsheet, nor having to figure out the best debts repartition. At that time, there were not so many web services for that purpose , few in french and none satisfying our needs. I used my recent skills with GWT, learnt Python and developped that : ...