I can't tell myself. A quick look at the source doesn't show any telltales like specific directories used by CMS'es. Neither do the RSS links as they should have a generator tag and there isn't one. Almost looks phpNuke-ish to me but there's nothing that sticks out as such.
Its not that easy to find which script they are using. But I think it must be a frame work in PHP. As I am not getting any errors when I call index.php. As they are usng the clean URLs it might not be joomla instead it can be drupal, CakePHP, Codeignitor, Zend some thing like that.