Wine now also has precompiled binaries available. Together with WineBottler (an application to prepare and pack Windows applications for redistribution with Wine), it is available here: http://winebottler.kronenberg.org/.

Wine is an application which allows to run Windows application on linux, BSD or Mac OSX. Rather than full emulation, it acts as a compatibility layer between the application and the OS.
Wine is not entirely foolproof just yet; there is still much to be done, but with each passing release, more and more applications are getting supported.