Darwine is a cross between WINE and Bochs that has recently sprung up:
Quoting them: The first phase is the port of WINE to Darwin/x86 with XDarwin (XFree86). While the basic compatibility is there, as Darwin is largely FreeBSD, we need to overcome the hurdle of its Mach kernel which uses the Mach-O format rather than ELF. The second phase is to then port WINE to Darwin/PPC and Mac OS X by integrating the Bochs IA-32 interpreter.
I initially thought this would take ages to get going, but with Apple's shift to Intel, there are people out there running this right now.