What is Project Centennial? It's a toolkit that enables developers to package and publish their existing .NET and Win32-based Windows applications to the Windows Store. Developers can also use Project Centennial tools to call common UWP APIs and services. You can read our in-depth "What is Project Centennial" feature here.
Looks like app developers will have the chance to tinker around with this tool very soon. Microsoft is reportedly looking to make Project Centennial bits available in the next Windows 10 Redstone Insider Preview build.
During day one of Microsoft's Build 2016 developer conference today, Microsoft made it quite clear -- Universal Windows Platform is the future and having Win32 apps in the Windows Store is a part of that strategy. Project Centennial seems promising; let's hope it delivers.