I just spent some time working with Eto.Forms (based upon your recommendation, thanks!). It looks pretty nice and seems straight-forward. I also appreciate that it officially supports F# in addition to the regular C# and VB.NET.
Unfortunately, it doesn't support .NET Core/Standard yet. The lead dev, Curtis Wensley (@cwensley), is currently working on supporting it and said that he hopes to have to completed in time for the Eto 2.4 release, per their Gitter chat (https://gitter.im/picoe/Eto?at=59d65ab4177fb9fe7e41ff9e).
Another interesting detail is that Avalonia seems to be using Eto's parser implementation. And Eto is (will?) using AvaloniaUI's (the parent of Avalonia) monomac implementation.
Unfortunately, it doesn't support .NET Core/Standard yet. The lead dev, Curtis Wensley (@cwensley), is currently working on supporting it and said that he hopes to have to completed in time for the Eto 2.4 release, per their Gitter chat (https://gitter.im/picoe/Eto?at=59d65ab4177fb9fe7e41ff9e).
Another interesting detail is that Avalonia seems to be using Eto's parser implementation. And Eto is (will?) using AvaloniaUI's (the parent of Avalonia) monomac implementation.