When we talked to TheCodingMonkeys at WWDC, they made a cryptic reference to an iPhone application they had in the works. They've finally revealed what they've been diligently preparing: Circulator, an iPhone application to help you track everything you lend and borrow.
TheCodingMonkeys are the brains behind SubEthaEdit and the open source utility, Port Map (TUAW coverage here). Most recently, they've been working with Boinx Software on the upcoming BoinxTV. They've found the time, somehow, to create what looks like a very useful addition to the growing collection of iPhone productivity applications.
Circulator lets you track the things you lend and borrow to and from your friends. It's not specific to any type of item; you can track everything from dollars and cents to DVDs and power tools. You can add images with the iPhone's camera or from your photo library and keep a history of transactions for repeat use. The portability of the application is what will make it the most useful; you'll be able to record that $20 you handed to your buddy right there in front of him, mercilessly crushing any hopes he had that you'd forget in a week.
What good would such an application be without the ability to automate the act of reminding your friends of such debts? Circulator can send an "overdue" SMS or email to debtors, with templates available for the tone of the reminder: nice, neutral or angry. Nothing says "I want my orbital sander back" like frequent, angry, software-generated emails. Of course, this kind of record keeping could also help friends stay friends by avoiding misunderstandings and unfounded accusations.
Circulator will cost $5.99 at the App Store. If you've lost track of more than six dollars worth of loaned items in your life, you might want to check it out. For more information and a video overview, visit the Circulator page at TheCodingMonkeys' website.