FriendsLend is an app that allows you to keep track of how much money you and your friends owe each other.
Record things such as a 'Quick IOU' between two people, someone paying a restaurant bill for a group of friends, a friend losing a bet on the golf course, or any other "I'll pay you later" scenario and let the app track the debt for you.
FriendsLend has an optional Groups feature, which can reconcile all the outstanding debts in the group and recommend the interpersonal payments required to settle the group in the most efficient way possible.
FriendsLend supports both an online (registered) mode, and a purely offline mode which does not require registration. In the online mode, you can add your friends that are also registered users, and receive alerts when they create IOU's with you. In the offline mode, you can keep track of your friends' debts for them by creating any number of offline people that you wish to track.