There's Eto.Forms (on github), which is an abstraction layer on top of WPF , WinForms , GTK and MonoMac / Cocoa - so you can get your own user interface on all platforms without the need for re-implementation for each platform. You do not need to suffer from the lowest common denominator, since you can implement the specifics for each platform (if desired, but not necessary).
, .NET , GTK WxWidgets, .