Epic's Unreal Engine 3 is one of the most critically acclaimed graphics engines and by gamers themselves, but so far the only Apple platform where it was present was on iOS.
Now Epic has updated the Unreal Development Kit to support Mac OS X, which means that most of the games that we see with this graphics engine will almost certainly support Mac when they are released.
Very good news without a doubt for all Mac users who like to play a game from time to time.
Source | Macrumors
They can be compiled for mac but udk is still windows, so you have to continue with unity3d which is still better than udk