GTKSharp

Gtk# or GTKSharp is a set of .NET bindings for the GTK+ GUI toolkit (similar to Windows Forms) and assorted GNOME libraries. The library facilitates building graphical GNOME applications using Mono or any other compliant CLR. Gtk# is an event-driven system like any other modern windowing library where every widget in an application has handler methods that get called when particular events happen.

GTKSharp binary for Windows exists for different versions in the external links.