We probably should have mentioned Linux explicitly but it's part of the very first diagram: .NET Core runs on many Linuxes, Xamarin runs on Android's version of Linux.

We highly care about making it easy to write code that works cross-plaform, especially on Linux. That's why we created .NET Standard!

I see that UWP is in the .NET Core box. Does this mean that we can or will be able to write GUI apps with UWP that target Linux?

No. Think of UWP as WinRT + .NET Core. While .NET Core is available for Linux, WinRT isn't. Within UWP the UI stack is provided by the WinRT side.

Xamarin has an abstraction layer for UI called Xamarin Forms. This will allow you share UI code across .NET Framework, UWP, iOS, and Android.

> rather than open up some of their coveted, proprietary codebase. (Winforms)

What makes you think that open sourcing WinForms would be any good? It's probably tied to Windows to the gills.

If anything, they should be doing something else, they should create or even better, support an existing UI toolkit and promote that as their cross platform UI.

While we haven't open sourced WinForms, there is a Mono version of Windows Forms. We've talked with the Mono guys about it and the general consensus was that the WinForms API shape doesn't make it very easy for cross-platform.

Is there any plan, even a low priority one, for picking up maintenance for something like Gtk# or Xwt or Eto.Forms? Or for extending UWP or Xamarin.Forms to Linux?

I agree, QT or GTK# would be a good start :)

Don't feed the troll folks, they need to learn to buy tinfoil on their own.