After 15 years of beta testing, development and various releases it's finally made v1.0.
Wine is 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.
http://winehq.org/?announce=1.0
For more reading.