The Windows UI Library 3, known shortly as WinUI 3, is a native UI framework that ships with the Windows App SDK. This is an SDK complementary to the Windows SDK, WPF, WinForms, and Win32. It provides a new unified set of APIs and tools that can be used to develop desktop apps on Windows 11 (as well as downwards to Windows 10, version 1809). I decided to have a look at what this framework provides and this post is written as I am trying it. To evaluate it, I’ll try to build a small application that does conversion between Celsius and Fahrenheit degrees as you type in a field.