It happens a lot. Go out to lunch with your friends and two or more people only have credit cards to pay with. One person ends up paying and then has to keep track of who they paid for. Then you end up not remembering about it and then never get that free lunch from that person.
IOU Lunch stops this by tracking who owes you lunch. Use this for dinners, lunch, breakfast, or whenever it fits to keep track of this information.
IOU Lunch will help you to remember who owes you a lunch and when it was. Delete the entry when you get repaid. It definitely beats using a pencil and paper because you always have your iPhone/iPod touch with you.