In a surprise move at the Build 2018 conference, Microsoft have announced that three key components of the Windows user interface are now open-sourced. Kevin Gallo, MS VP for the Windows Developer Platform sums it up in a blog entry. https://blogs.windows.com/buildingapps/2018/12/04/announcing-open-source-of-wpf-windows-forms-and-winui-at-microsoft-connect-2018/ [windows.com]
The newly opened-up components are critical for writing desktop applications and have so far been Windows-only. Based on C# and the .NET framework, especially WPF is generally considered to be reasonably good. Interest from beyond the Windows ecosystem might appear: when will we see ports to the Linux and Mac platforms, and what would it mean to their platform-specific toolkits GTK and Cocoa?