haXe/PHP is an extended version of the haXe compiler with a new platform target: PHP of course.
Why haXe/PHP? One of the biggest concerns in using haXe as a language for the server-side development is that you probably must install new software on the web-server (Apache mod_neko or some kind of JavaScript engine). This is not an option on many “cheap” (and not so cheap) hosting services while PHP is almost globally available.
haXe/PHP is now officially part of haXe. It is still considered experimental. In any case you can find it in the haXe website.
String and Array are used as native values and are not encapsulated in objects. This makes the PHP code prettier and faster but as a drawback you can encounter inconveniences when those types are used as Dynamic (ex: Reflection).