Owners of Intel-based Macs can now test the first Beta release of Crossover Mac. Crossover Mac is Codeweavers' port of Wine (windows emulator) which was originally wrtitten for Linux, which was then subsequently ported over to Darwin under the monicker Darwine.
Once installed, Windows applications will run windows-based applications under OS X without the need to install a virtual machine (such as Parallels) or to re-boot (to actually boot into Windows via Boot Camp). Initial reports say that installation of Crossover Mac is a bit kludgy and that it does not really work too well at this point. However, this is just minor setback because I'm pretty sure that once its ready for primetime, Crossover Mac would be the ideal solution to the problem of running a Windows application without actually installing and using Windows.