In terms of maturity and feature-completeness, GTK# is the answer. Unfortunately, it's no beauty either. Especially on Mac it does its own control rendering an

In terms of maturity and feature-completeness, GTK# is the answer. Unfortunately, it's no beauty either. Especially on Mac it does its own control rendering and, while it tries to match the OS, has problems. XWT was meant to replace GTK# and has some good underpinnings but it doesn't seem super active right now.