William is spot on, you'll need very little AJAX on the website, while most of it will be down to, typically, PERL as PERL can read raw HTTP headers, while PHP is somewhat limited there unless you use a PHP stream-wrapper like so:
PHP Code:
$szData = file_get_contents('php://input');
Although PERL is definitely the way forward. But to answer your question directly, I know of no such
free script that would suit your requirement.