Formphp-xajax is a project mainly written in PHP, it's free.
Formulario de contacto en PHP usando XAJAX
formphp-xajax es un ejemplo de formulario usando php y xajax adicionalmente se utiliza la libreria recaptcha de google.
2011 Jorge Brunal a.k.a. Diniremix
The reCAPTCHA PHP Lirary helps you use the reCAPTCHA API. Documentation for this library can be found at
http://recaptcha.net/plugins/php