Porting Kit is an application which ports Windows games so you can play it on your Mac without needing Windows. Sound pretty cool, and it sure is. But how does it work, is it free and legal? Well, those questions and more I will try to answer on this page. Porting Kit uses Wineskin wrappers to create its ports. Wineskin mainly use the free open-source code Wine.
Wine is a piece of software that in difficult words is a 'compatibility layer capable of running Windows applications on several POSIX-compliant operating systems, such as Linux, Mac OSX, & BSD. Instead of simulating internal Windows logic like a virtual machine or emulator, Wine translates Windows API calls into POSIX calls on-the-fly, eliminating the performance and memory penalties of other methods and allowing you to cleanly integrate Windows applications into your desktop.' So its not an Windows emulator but it makes it possible to run Windows software on your Mac.
In combination with the free Wineskin (an graphical shell around Wine), Porting Kit will fulfill your game wishes on your Mac. Wine is under constant development and every 2 weeks Wine gets a new release with updated code which adds more features and fixes problems in earlier versions. This makes it possible to update existing ports in the Porting Kit for better performance and bug fixes, and new games which didn't work before.