Wine (Wine Is Not an Emulator)

Wine can be thought of as a Windows emulator for Mac OSX and Linux systems capable of running almost all Windows programmes on a different operating system. It’s Windows as a ‘programme’ rather than an operating system, which makes it perfect for Linux or Mac OSX users that need to run a “Windows Only” programme without paying for an entire Windows operating system.

As usual it has an excellent wiki here and can be downloaded free here for most operating systems.