I've tried nimx one of the first, it works fine with OSX but is far from native :(
Actually threre is one wrapper: <https://github.com/SSPkrolik/nim-native-dialogs>, it emits Objective-C commands directly to Cocoa API, as I understand. It works perfect but only for two things: file open and save windows. Just thinking if it is possible to wrap all Cocoa API such direct way?