I ported a popular Google application from Windows to OS X using Qt Designer (and Qt in general) a number of years ago. Qt is really good for quick bringup of

I ported a popular Google application from Windows to OS X using Qt Designer (and Qt in general) a number of years ago. Qt is really good for quick bringup of a cross platform app, and Designer and its associated code generator does a good job of generating reasonable UI's. Swift didn't exist at the time, but the combination of InterfaceBuilder and Cocoa was amazing. Where things start to get tricky is that Qt has to reimplement a lot of widgets themselves, on account of their target platforms being quite different from each other, so you end up with a slightly non-native feel on each platform, and some behaviors are subtly different. Things have gotten better since then, but that non-native behavior is still there. These behavioral differences aren't too bad on Windows and X11, since those platforms have a lot of inconsistency between apps, but mac users expect the mac to "feel" a certain way, and Qt is a little different, so we got a _lot_ of feedback, some of which I still remember - "Google Earth looks like it fell out of the ugly tree and hit every branch on the way down". The tradeoff you have with a cross platform toolkit like Qt is quick bringup of a cross platform app, versus later chasing down a lot of platform differences causing problems, and that slight non-nativeness. The alternative is to write your UI natively on each platform and abstract away the functional core from the UI, which is a lot more work but works better. If I was building a UI for major public consumption today, I would go with the extra work of native UI. If I was building tooling for my own developers, hands down, I'd use Qt.