Wine is an implementation of the Windows API on top of X and Unix. It does not require Microsoft Windows, but can use native Windows DLLs if they are available. It provides both a development toolkit for porting Windows source code to Unix as well as a program loader, allowing many unmodified Windows programs to run on x86-based Unixes.
minor feature: Support for using LLVM-MinGW as PE cross-compiler. Better reporting of error location in JScript and VBScript. Support for relocatable installation of the Winelib tools. Ellipse drawing in Direct2D. OLE monikers improvements. Various.