Unfortunately, most good trading platforms are not written for Macs. Nevertheless, some traders that I know have been able to run the simulator on a Mac using a special program.
Even though most trading software out there is written for Windows and not for Apple, there are supposed to be software programs that allow Mac users to be able to run Windows programs on their computers. I do not have any experience with them, so I cannot recommend any of them. I believe that Microsoft has a program called Virtual PC that can be installed on the Mac operating system to create an emulated Windows-compatible computer.