You know the modules from %INC. It seems you want to know the packages in use. That can be done by visiting the symbol table tree.

use strict;
use warnings;

sub visit {
   my ($parent, $table) = @_;
   for (keys(%$table)) {
      if (my ($trimmed) = /^(.*)::\z/s) {
         next if $_ eq 'main::';
         print("$parent$trimmed\n");
         visit("$parent$_", $table->{$_});
      }
   }
}

visit('', \%::);
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The presence of &new, @ISA or &DESTROY would be a good indicator that the package is a class.