Unreal Tornament 2003
Of note, Rein stated that there were no specific plans for a Mac version of Unreal Tournament 2003, and also citing the OS X/9 divide:
No I don't get fed up about that. Unreal and UT did really well on Mac but now with the fractured Mac situation once again (OS9 vs. OS X) it's hard to see it as being worth the effort. But Macsoft seems interested and I'm confident it's something we'll get done down the road.
Recent rumors suggest that future Macs may not be able to boot into OS 9. Such a move would presumably accelerate OS X adoption and software migration.