Is there any games that are only avaliable on the Mac and not Windows ?
Pangea Games used to make Mac-only games.
And there is an Intel version of Escape Velocity: Nova, which has expansion packs with the contents of the previous two EV games.
There's actually a windows version of EV: Nova.
Ambrosia published my favorite platformer, Ferazel's Wand, which was Mac-only. I'm really sad it never got an OS X port.
Then there was Marathon, not sure if that had a Windows release or not.
Wow! What memories... you just reminded me of all the old AppleTalk (Mac networking) games!