From Mac Guides
WINE is an open source project that allows x86 Windows applications to run on Unix-like operating systems. Its name is derived from the self-recursive acronym Wine Is Not an Emulator, although unofficially it has been expanded as WINdows Emulator.
The WINE developers describe it as "a translation layer (a program loader) capable of running Windows applications on Linux and other POSIX compatible operating systems. Windows programs running in WINE act as native programs would, running without the performance or memory usage penalties of an emulator, with a similar look and feel to other applications on your desktop." 
In February 2006, it was reported that the first versions of WINE for Intel Macs had been compiled and were running, albeit with limited compatibility.
WINE is now well supported in the main WINE branch. Darwine project is basically dead, and no longer needed as normal WINE runs fine on Mac OS X.
There is not currently a binary install for WINE for Mac OS X, it can only be installed from being compiled from source code, and then it is all command line usage.
There are several 3rd party programs that use WINE on Mac OS X though, such as Wineskin, WineBottler, Crossover, and PlayOnMac, that are GUI controlled and do not require compiling or command line usage.