This pattern provides an easy to decouple many components working together. It is a good alternative over Observer IF you have a "central intelligence", like a controller (but not in the sense of the MVC).
All components (called Colleague) are only coupled to the MediatorInterface and it is a good thing because in OOP, one good friend is better than many. This is the key-feature of this pattern.
You can also find these code on GitHub
MediatorInterface.php
MediatorInterface.php
Mediator.php
Mediator.php
Colleague.php
Colleague.php
Subsystem/Client.php
Subsystem/Client.php
Subsystem/Database.php
Subsystem/Database.php
Subsystem/Server.php
Subsystem/Server.php
Tests/MediatorTest.php
Tests/MediatorTest.php