Microsoft open source

https://referencesource.microsoft.com/

https://github.com/dennismagno/metroframework-modern-ui

https://github.com/dotnet

https://github.com/Microsoft

https://github.com/OfficeDev

https://github.com/aspnet

 https://github.com/Microsoft/Windows-classic-samples

https://github.com/dotnet/winforms

https://github.com/dotnet/wpf

https://github.com/Microsoft/WPF-Samples

https://github.com/apress/pro-wpf-4.5-in-csharp

https://github.com/MaterialDesignInXAML/MaterialDesignInXamlToolkit

https://github.com/Windows-XAML

https://github.com/MahApps/MahApps.Metro

http://microsoft.github.io/windows/

https://github.com/Microsoft/microsoft-ui-xaml

https://github.com/SoftEtherVPN/SoftEtherVPN

 https://github.com/MicrosoftDocs

Microsoft open-sources WPF, WinForms, and WinUI XAML
GitHub: WPF https://github.com/dotnet/wpf
, Windows Forms https://github.com/dotnet/winforms
, and WinUI https://github.com/Microsoft/microsoft-ui-xaml
.

Microsoft open-sources WPF, WinForms, and WinUI XAML

https://msdn.itellyou.cn/

http://www.imsdn.cn/operating-systems/windows-10/