PEAR::XML_Wddx, http://pear.php.net/package/XML_Wddx PHP's wddx extension (--enable-wddx) PEAR::XML_RPC, http://pear.php.net/package/XML_RPC Useful Inc's XML-RPC, http://xmlrpc.usefulinc.com/php.html PHP's xmlrpc extension (--with-xmlrpc) More implementations: http://www.xmlrpc.com/directory/1568/implementations PEAR::SOAP, http://pear.php.net/package/SOAP NuSOAP, http://dietrich.ganx4.com/nusoap/ PHP5's SOAP extension (--enable-soap)