Mac OS X has been around for over a decade, and has evolved considerably since it first debuted in 2000 as a public beta. TwistedMac has put together a fantastic (and very detailed) article showing and comparing each version of OS X.
…spanning a decade and OS X (pronounced as “O”-”S”-”10″ not “O”-”S”-”X”) has gone through nine (9) major OS revisions of OS X to date including Public Beta. In this review I’ve pointed out the release information for each major version of OS X as well as snapshots to help show the differences from version to version of OS X.
From the very beginning, to the the transition from Mac OS classic to OS X, right up to Apple’s recently announced OS X 10.8 Mountain Lion, the article covers all of the bases, and is definitely worth a look. I highly recommend checking it out!