Nowadays it's important to support a whole zoo of platforms and devices, while .NET Core and .NET Standard substantially help with the portability of C# code between them. But every platform has its own development tools, and most of them are stuck in the times of MFC and Windows Forms, lacking a proper C# integration. There is a number of solutions trying to get the platforms to a "common denominator" and add an adequate support of MVVM and XAML layout, but all of this... just doesn't quite get there.
.NET developers are used to stylizng controls wherever and however they want, with good coupling lists to the collections, rich system of bindings. And that's what project AvaloniaUI is trying to achieve by evolving WPF ideas in the open source world. It's a challenging journey where a lot has to be made. What has been accomplished, what you can already use and what challenges arise while developing a project like that — a talk by one of the project members.
Nikita has a vast experience developing for a broad spectrum of platforms (starting with WinCE) using a whole zoo of technologies and is happy to share that experience.