Consumers encounter a Facade when ordering from a catalog. The consumer calls one number and speaks with a customer service representative. The customer service representative acts as a Facade, providing an interface to the order fulfillment department, the billing department, and the shipping department. Remember that Adapter makes two existing interfaces work together as opposed to defining an entirely new one. Whereas Flyweight shows how to make lots of little objects, Facade shows how to make a single object represent an entire subsystem.
Mediator is similar to Facade in that it abstracts functionality of existing classes.
In contrast, Facade defines a simpler interface to a subsystem, it doesn't add new functionality, and it is not known by the subsystem classes. Abstract Factory can be used as an alternative to Facade to hide platform-specific classes.