Passbook, "for the stuff you have in your pocket," is a Google Wallet competitor, and potential killer. Passbook does not rely on near-field communications (NFC) or other static hardware, like Google Wallet and other payment systems do. It doesn't rely on vender partners to support specific payment methods. Instead, using QR and other types of barcodes, Passbook collects receipts, discount cards, tickets, and boarding passes and then displays them on your iPhone screen so they can be scanned by retailers at the time of purchase or redemption.
Unfortunately, Passbook is very unfinished--aside from our one screenshot, the application is pretty much non-functional. I look forward to learning how Apple plans to collect my "data"--all my receipts, tickets, and passes--so I can take them with me on my phone. Will it be via camera, email, file sharing, or all of the above?