If you end up with a running tally of bills (either splitting or alternating or what have you), I'd recommend SplitWise to keep track of who owes what to whom.

If you end up with a running tally of bills (either splitting or alternating or what have you), I'd recommend SplitWise to keep track of who owes what to whom. It also has a simplify debts feature so that if you owe X to a friend and a friend owes Y to you (where X>Y), the friend who owes you can just pay the friend whom you owe directly. It also works great for rent, utilities, pizza, etc. in a room mate situation which is mentioned in the original article.