Some people like to refer to OS X as UNIX-like when it’s actually a UNIX. There was a time when it was UNIX-like and some people liked to refer to it as a UNIX, but it’s not now.
OOP the Easy Way
Object-Oriented Programming the Easy Way: a manifesto for reclaiming OOP from three decades of confusion and needless complexity.APPropriate Behaviour
APPosite Concerns
FSF