Codeigniter template library and HMVC ( mx library ) the static method run()
<?php
class Test extends MX_Controller {

    public function __construct()
    {
        parent::__construct();
        $this->template->title($this->config->item('site_name','app'));
    }

    public function index()
    {
        $this->template->build('index');
    }
}

<?php
//ms module
class Msrofi extends MX_Controller {

    public function __construct()
    {
        parent::__construct();
        $this->template->title($this->config->item('site_name','app'));
    }

    public function index()
    {
        $t = Modules::run('test/test/index');
        var_dump($t);
        $this->template->build('index_message');
    }
}

class Test extends MX_Controller {

    public function index()
    {
        // This path works only from the "test" module
        // $this->template->build('index');

        // This path works from any module
        $this->template->build('test/index');
    }
}

ob_start();
Modules::run('test/test/index');
$t = ob_get_clean();
var_dump($t);