wine -- A Windows 16/32 bit emulator.
http://www.winehq.org/
While Wine is usually thought of as a Windows(TM) emulator, the Wine developers would prefer that users thought of Wine as a Windows compatibility layer for UNIX. This package includes a program loader, which allows unmodified Windows 3.1/95/NT binaries to run under Intel Unixes. Wine does not require MS Windows, but it can use native system .dll files if they are available.