Working code example of PHP XML-RPC connex to site?

How complex do you want the example to be?

This outputs “Hello”.

$client = new WP_HTTP_IXR_Client('http://example.com/xmlrpc.php');
$client->query('demo.sayHello');
echo $client->getResponse();

This outputs “9”.

$client = new WP_HTTP_IXR_Client('http://example.com/xmlrpc.php');
$client->query('demo.addTwoNumbers', 4, 5);
echo $client->getResponse();

This gets the WordPress version:

$client = new WP_HTTP_IXR_Client('http://example.com/xmlrpc.php');
$client->query('wp.getOptions', 0, 'username', 'password', 'software_version');
$response = $client->getResponse();
echo $response['software_version']['value'];

Source: Me, 4 years ago:
http://ottopress.com/2010/wordpress-3-1-and-xml-rpc/