.swf

A SWF is a file used by The Club Penguin Team when designing rooms and designing player cards. When you log into an SWF room the room is empty.

History
When Club Penguin started the only SWF's where the rooms.

There also is a Dark Black penguin called SWF Test, made by the Club Penguin Team he is used for testing and squasing bugs, he usally appears on Sabertooth.