Wine (Wine Is Not an Emulator) allows MS-Windows applications to run under X Window System in any Linux or Unix system on an x86 computer. Wine provides the API´s needed to run Windows 3.x or Windows 95 applications.
Wine also provides a library of API´s that may be used to compile MS-Windows source, resulting in an executable that will run natively on Unix running X Window System.
The Wine Project itself is an Open Source project. Wine Development began in 1993. Developers are spread over the whole world.