I don't know much about Mac; but a friend of mine seems to appreciate the environment they offer.
TerryP covered most of the basics, and then some.. but from the GUI aspects of things, the main Apple tookit (Cocoa) is an OpenStep implementation. (
..and then some.)
While I don't recommend much of anything from GNU land, the GNUstep project does claim to support some of those Apple extensions.
Good luck.. I wouldn't wish dial-up access on anyone, my 10Mbit line keeps me happy.
