Unlimited number.
You can implement as many as you want.
I implemented TheCache, ACache, MyCache, YourCache, OurCache, DefaultCache, NonDefaultCache.
I started with nullCache in File NullCache, but a camel refused to compile it. That was my first camel case.
Currently I am refactoring SimpleCache to ComplexCache, but it got so complicated that I fear I will never finish it.
:-)