Web/iOS/Android/Windows 8: It's easy to lose track of small favours we need to return or debts that we're owed. I Owe You makes it easy to keep a running list from any device.
The service keeps things pretty simple. You log onto your account on the web or through a native app, and add debts that you owe to others, or debts that others owe you. Each entry has fields for a description, due date, person, payment installments, and amount, but they're all optional, so you just need to enter what will help you remember. Once your debt is entered, it will sync to I Owe You's servers so you can pull it up anywhere.
I Owe You's sharing features are fairly limited. You can create contacts in the app and share debts to that person's email address, but you can't import your contacts from any other service. This is probably better-suited as a private ledger to keep track of your debts on multiple devices.
A basic I Owe You account is free, as are all of the apps. Pony up $US2.49/month for the pro version, and you'll get to remove ads and export your data to an Excel file.