gistfile1.php

<?php

class App
{
    public $callables = [];

    public function __construct()
    {
        register_shutdown_function([$this, 'run']);
    }

    public function run()
    {
        foreach ($this->callables as $callable) {
            $callable();
        }
    }
}

$app = new App();
$app->callables[] = function() { echo 'yay'; };
$app->callables[] = function() { echo 'foo'; };
$app->callables[] = function() { echo 'bar'; };