I've been messing with Eto.Forms recently. You define everything through code (or optionally in a JSON blob) rather than in a designer, and it tries to use nati

I've been messing with Eto.Forms recently. You define everything through code (or optionally in a JSON blob) rather than in a designer, and it tries to use native controls to display your design. It's pretty solid and easy to use and I'm quite happy with it. If you want an exquisite, beautifully-designed OS X app then you should be looking into having separate frontends per platform anyway, but having tried Eto I find it fits my needs. It's much better than I expected.