macOS/OSX comes with tools that make it super easy to write native GUI applications with Applescript and Perl! This example uses the cool and free Robtex API to validate Autonomous System Numbers for networks in the global BGP table. Applescript provides plenty of ways to collect and display data, handle errors, and can launch terminals and text editors or any app and automate the entire operating system GUI while Perl does pretty much anything else you can imagine.

Start : Applications -> Automator
Select: File -> New
Select: Application

We're going to create an application but Automator can also encapsulate Perl into a Service, Image Capture Plugin, Dictation Command, Folder Action, Calendar Alarm, Print Plugin or Workflow.

Now that Automator is open click the Library icon or select View -> Show Library.

Select: Actions -> Utilities -> Run AppleScript (double click it)

Replace the default code with this:

(* Demonstration MacOS/OSX app in AppleScript and Perl *)
(* Posted at perlmonks.org by Anonymous Monk 6/13/2018 *)
(* Node: How to write apps for macOS/OSX in Perl!      *)

repeat
    repeat
        try
            set ASN to text returned of (display dialog "Autonomous Sy
+stem Number:
(Example: 714 is Apple Inc. 666 does not exist. Blank to exit.)" with 
+title "Perl ASN Check" default answer "" buttons {"Check"} default bu
+tton 1)
            set ASN to ASN as number # require a number
            exit repeat # continue if ASN is numeric
        on error # not a number?
            display alert "Please enter an Autonomous System Number!" 
+as critical
        end try
    end repeat
    
    if ASN is equal to 0 then return # exit if blank
    
    # ALL MACS HAVE PERL BABY!
    set RES to do shell script "
        perl -MHTTP::Tiny -e '
            my $r = HTTP::Tiny->new->get(q~https://freeapi.robtex.com/
+asquery/" & ASN & "~);
            if (length $r->{content}) {
                $r->{content} =~ /[0-9]+\\.[0-9]+\\.[0-9]+\\.[0-9]+/
                ? print q~ASN Exists!~ : print q~ASN Not Found!~;
            }
            else {
                print q~Download failed!~
            }
        '
    "
    display alert RES
end repeat
[download]

Save the application and double click its icon in finder. BEHOLD! Perl apps for macOS/OSX!!!

(Tips: In the Perl code avoid single quotes and be prepared to do some extra backslashing.)