MinGW: Minimalist GNU For Windows
MinGW, also known as mingw32, is a collection of header files and import libraries that allow one to use the GNU Compiler Collection (GCC) on Windows systems. Unlike toolsets like Cygwin, it can produce native Windows32 programs that do not rely on any 3rd-party
DLLs. MinGW uses Microsoft standard runtime libraries such as CRTDLL.DLL which is available on all Win9x/NT systems or MSVCRT.DLL which is a part of all Win9x systems since the original Win95 release and of all NT systems. The current toolset includes GCC, GNU Binary Utilities (Binutils), GNU debugger (gdb) , GNU make, and some other utilities.
With the basic package, you can write console-mode ANSI compliant programs using GCC, but if you want to access the features provided by the Windows32 API, you also need the w32api package.
Many common utilities, libraries etc. have been ported to Windows using MinGW. Some examples: Perl, ssh, Lynx, SDL... More information, downloads and mailing lists can be found at http://www.mingw.org/