Microsoft's Project Reunion aims to streamline Win32 and UWP app development on Windows 10

Windows apps
Windows apps (Image credit: Windows Central)

What you need to know

  • Project Reunion combines Win32 and UWP app development.
  • It provides a common API platform for new and existing apps.
  • Any apps on Windows 10 are now just "Windows apps."

Microsoft is closing the gap between Win32 and UWP app development with Project Reunion, an effort to componentize the Windows API and UWP API so developers can modernize and build apps that work across all versions of Windows 10. In the past, app development on Windows 10 has been clear cut with two options; a classic Win32 app using the Windows API, or a modern universal app with UWP APIs. With Project Reunion, all apps are just "Windows apps."

The Redmond-giant has been pushing this idea since Build 2019 but is now formalizing the movement with Project Reunion. The company says this new effort will streamline app development across supported versions of Windows 10.

For the past couple of years, we have been breaking down the barrier between Win32 (also called the Windows API) and Universal Windows Platform (UWP) APIs. Project Reunion expands this effort to make it easier to build a great Windows app. It will unify access to existing Win32 and UWP APIs and make them available decoupled from the OS, via tools like NuGet. This will provide a common platform for new apps. Plus, it will help you update and modernize your existing apps with the latest functionality, whether they're C++, .NET (including WPF, Windows Forms, and UWP) or React Native. As we decouple existing APIs and add new APIs, we are also doing the work to polyfill, as needed, so the APIs work down-level across supported versions of Windows.

Project Reunion is an evolution of the Windows developer platform that will make it more agile, modern, and open. Projects like WinUI 3 and WebView2 are already part of the Project Reunion journey, allowing developers to take advantage of new, modern APIs on either UWP or Win32 built applications.

In layman's terms, Project Reunion makes it so developers can build apps that have the latest OS features without having to worry about older versions of Windows 10. Developers can compile the newest APIs directly into their apps instead of depending on the OS itself to have them.

Microsoft is pushing the idea that there's no such thing as a Win32 or UWP app, and that everything that runs on Windows 10 is just a "Windows app." The idea is that it doesn't matter which framework developers use, as long they use APIs that are native to Windows. In the future, users shouldn't be able to tell the different between a Win32 or UWP app. If it runs on Windows, it's just a Windows app.

The effort will streamline how developers modernize existing apps and create new ones by reducing fragmentation between the Windows API and Universal Windows Platform. It will provide a common, backward compatible platform for existing code and for the latest client platform innovations.

It's going to be interesting to see if Project Reunion helps bring legacy Win32 programs forward with more modern interfaces and features unique to Windows 10. Microsoft would like all legacy apps to take advantage of efforts such as WinUI 3, and Project Reunion should help push that forward. What are your thoughts on Project Reunion? Let us know in the comments.

Zac Bowden
Senior Editor

Zac Bowden is a Senior Editor at Windows Central. Bringing you exclusive coverage into the world of Windows on PCs, tablets, phones, and more. Also an avid collector of rare Microsoft prototype devices! Keep in touch on Twitter and Threads