I'd like to add to this thread that games like Baldur's Gate II and Planescape Torment (games using the Infinity Engine) are more or less playable on the Mac with the
GemRB engine. Even though there are no binary releases, it is possible to compile it on the Mac with few code changes.
Admittedly, Planescape Torment which I was interested in didn't run too smooth, and Baldur's Gate is available for the Mac anyway.
I love the project though, stuff like that is pretty hard to reverse engineer, kudos to the devs.