First, Apple still has a X11 server on MacOSX, so you can just compile and run your X application there. Otherwise, learn Objective-C and Cocoa, and rewrite th

First, Apple still has a X11 server on MacOSX, so you can just compile and run your X application there. Otherwise, learn Objective-C and Cocoa, and rewrite the user interface. Works better when the application is well modularised to begin with.