Microsoft is introducing universal Windows apps, a way for developers to create a single app that works across Windows phones, tablets, PCs, and the Xbox One. "All of us want the same app experiences across all devices," David Treadwell, a Microsoft operating system executive said while introducing the new type of apps. "Yet today there’s no easy way to create apps that work across all form factors."

"I don't have to buy a different app for the phone and the PC."

That's changing within Microsoft's ecosystem, as Treadwell demonstrated on stage at Microsoft's Build developer conference while showing features coming in Windows 8.1 and Windows Phone 8.1 updates. Microsoft says that this should be easy for developers to implement, as much of the code can be reused across the different platforms. Of course, the biggest benefit may be the simplicity for users: "I don't have to buy a different app for the phone and the PC," Treadwell said. And because it's a single app that's running across all screens, everything handled by the cloud should sync across them, including notifications and in-app purchases.

Microsoft's tools will allow developers to tweak a single app's interface based on both the form factor that it's running on and whether it's being used with or without a mouse and keyboard. Demonstrating how it's done using Visual Studio, Kevin Gallo, Microsoft's developer ecosystem director, said that developers will be able to "do some tuning to make apps pop on each form factor." On the Xbox One, developers will also be able to tweak their apps to work with the controller and Kinect.

Though a single app can run across all four platforms, you may have to pay for access to the different platforms separately. Microsoft said that developers could require a user to pay for their app on both a phone and PC or have a single purchase grant access to them both. While that may not thrill users, it should allow developers to avoid the trouble of splitting up apps — which has been a recurring problem for developers on iOS.

Allowing apps to run across all of its platforms has appeared to be a goal of Microsoft's for some time now, and it's a powerful move now that it's here. If it works as well as Microsoft says it does, this could allows users to easily move their work or progress from one screen to another without effort. It could also encourage developers to bring their apps to Microsoft's less used platforms, helping to flesh out their app offerings. It's a major change for Windows and Xbox, and the end result will likely be a more seamless experience for users of multiple Microsoft platforms.