Microsoft's Windows Phone 8.1 apparently comes with native support for Apple's Passbook. The app, introduced back in iOS 6, is Apple's fancy way of displaying your loyalty cards, movie tickets, boarding passes and more. But because of how it's designed, Microsoft was able to easily get the experience up and running in Microsoft Wallet, which is available in the developer preview of Windows Phone 8.1 and was first introduced in Windows Phone 8.
As explained by iMore, Passbook cards are simply collections of data presented in a easily digestible way; the Passbook app itself acts as a projector of that information.
What Microsoft is doing is taking that data, rendering it, and then pushing it to Microsoft Wallet. The experience is largely identical to what you'd get through Passbook on iOS. The only hurdle to Microsoft's plan is that Passbook on iOS provides the ability to update cards, so if your flight's gate number changes, you might not know about it on Windows Phone 8.1. iMore notes that Apple also code-signs Passbook cards, and it isn't clear at this point of Microsoft is accepting Apple certificates or just saying yes to any pass regardless if there's a signature or not.
Since Passbook featured prominently during the announcement of iOS 6, chances are Apple won't take too kindly to Microsoft's loophole. Sure, Apple could keep Passbook open and ultimately bring wider exposure to the feature. But this is Apple and Microsoft we're talking about, two competing entities trying to wrestle market share away from each other. It's unlikely you'll purchase a Windows Phone 8.1 device with Passbook in mind. But if the support remains, it wouldn't be such a bad thing for consumers.