OS X Native full on IDE
AFAIK Xcode can support web languages with some plugins, but all the informations I have are pretty old. http://web.archive.org/web/20110811093439/http://developer.apple.com/internet/scripting/phpappledevtools.html

And there are some projects to support autocomplete for PHP that I never really tried.
https://github.com/tonyjohnston/PHP-Xcode-Autocomplete

I'm very happy about PHPStorm, btw and I don't feel the need for a native IDE after moving to it from Eclipse/Aptana.