I just used Julia to make build scripts. We had an app that needed to be secure so we did all sorts of things with obfuscating code, hardening, custom signing of executable. I have forgotten a lot of it. It started out as a complex Bash script which I hated.

Porting to Julia made it run way faster and the code was much easier to read. Julia is just awesome for scripting. Sure it is a bit slower to startup but unless your script runs for a very short time, Julia will be much faster.

For UI development I have actually stuck to Swift thus far, even though I might prototype algorithms and stuff in Julia and port them over.

However I did make a Julia Package ObjCWrap.jl which allows you to call Objective-C from Julia so in principle you could develop Mac applications. It was derived from work Mike Innes did years ago before Julia 1.x

You can check it out here: https://github.com/ordovician/ObjCWrap.jl

It still needs more work to be a good solution though. I have not made a good match for structs. Fortunately they are not used that much in Objective-C so you could get away with some custom wrapper. Except I never made those.

I have been pretty happy with Gtk so I have not prioritized developing this further. A good Julia solution would need something I think to take care of the boilerplate stuff that Xcode solves today when setting up user interfaces.