A CPPS, or Club Penguin Private Server, is a privately owned version of Club Penguin. They were the main source of Club Penguin after its shut down.
CPPSes
Here is a list of the current Club Penguin CPPSes: (If there is one not here, add it, and even add a page)
OldCP
CPO
CPPSme
CPR
CPio
Oasis