In my opinion, the best release is probably Raphsody DR1, released in
September 1997. This was the first OS release from the recently
merged Apple-NeXT, and was the first version of NEXTSTEP (aka
NeXTStep aka OPENSTEP) in a Macintosh skin.
While that system wasn't stable (some would claim that the first
stable Mac OS X release was 10.2) or highly useful, it was the
transition from the aging "Classic" Mac OS to a more modern platform.
For while the old OS was highly respected, UI wise, it's internals
were more suitable for the eighties, when one would pay $3000 for a
computer that was less powerful than a 3 years old cell phone.
Not that UNIX, with it's root in the 1970s is a modern OS: but it's
much more scalable, and much more suitable to exercise the
supercomputer we currently call "home computers".
And besides, UNIX has much more hacker cred: I doubt any other OS
would make me "switch" from my hand-built Linux throne, and become a
drooling Mac-fanatic like the ones I used to laugh at only seven years
ago (though I wonder what will happen if I'll travel back to 1995, and
tell Mac users then that in less than a ten years time, every new
Macintosh computer would come with a command line and a copy of
Emacs).
The Great Tiger Giveaway