This class will take a Mongo connection object (see http://php.net/mongo), determine the type of connection (single server, replica set, sharded) and recursively connect to each server to determine some basic details about the server (version, hostname, port, memory utilization, etc).
<?php
require_once('mongo/Stat.class.php');
$mongo = new Mongo('mongodb://127.0.0.1:27017', array('replicaSet' => false));
$info = Mongo_Stat::getConnectionDetails($mongo);
var_dump($info);