user did something.php

<?php

class User {
    public function __construct($name) {
        $this->name = $name;
    }
    
    public function getName() {
        return $this->name;
    }
}

class ActivityService {
    const EVENT_ACTIVITY = 'activity';
    
    protected $evm;
    
    public function __construct(User $user) {
        $this->user = $user;
    }
    
    public function getEventManager() {
        if (! $this->evm) {
            $this->evm = new EventManager();
        }
        
        return $this->evm;
    }
    
    public function trigger($actionObject) {
        $this->getEventManager()->trigger(self::EVENT_ACTIVITY, array(
            'user' => $this->user,
            'object' => $actionObject,
        ));
    }
}

class ActivityMessageStrategy {
    public function createMessage(User $user, $object) {
        if ($object instanceof StdClass) {
            return sprintf('User %s created a standard class, great for him', $user->getName());
        }
        
        return sprintf('User %s did an unkown action, shame', $user->getName());
    }
}

class ActivityListener {
    public function __construct(ActivityMessageStrategy $strategy) {
        $this->strategy = $strategy;
    }
    
    public function respond(EventInterface $event) {
        $user = $event->getParam('user');
        $object = $event->getParam('object');
        
        echo $this->strategy->createMessage($user, $object);
    }
}

// in onBootstrap()
$service = $sm->getServiceLocator()->get('activityService');
$service->getEventManager()->attach(ActivityService::EVENT_ACTIVITY, array(new ActivityListener(), 'respond'))

$user = new User('Mike');
$service = new ActivityService($user);

// in application
// user creates a class (silly example), eq. do something
$object = new StdClass();

// and notify everyone about that
$service->trigger($object);