Run Windows, Linux and a lot more Systems on your Mac. Q is a feature packed cocoa port of QEMU: Switch fast between guest PCs. Save and restart guest PCs at any stage. Easily exchange Files between Host and Guest. Q makes use of OS X most advanced technologies like openGL and coreaudio to accelerate your experience with your guest PC.
This is "only" an easy-interface to QEMU, «a generic and open source processor emulator which achieves a good emulation speed by using dynamic translation», but it works very very good (and smarty, imho).
If you need a good and rich System-Emulator (it support x86, x86-64, PPC PowerMac, PPC PREP, Sparc32, MIPS right now!) on your Mac, give its a chance!