Cygwin
Cygwin is a Linux-like environment for Windows. It consists of two parts:
* A DLL (cygwin1.dll) which acts as a Linux API emulation layer providing substantial Linux API functionality.
* A collection of tools which provide Linux look and feel.
The Cygwin DLL works with all non-beta, non “release candidate”, ix86 32 bit versions of Windows since Windows 95, with the exception of Windows CE.
The Cygwin tools are ports of the popular GNU development tools for Microsoft Windows. Cygwin can be expected to run on all modern 32 bit versions of Windows, except Windows CE. This includes Windows 95/98/ME/NT/2000/XP/2003 and the WOW64 32 bit environment on released 64 bit versions of Windows. Parts are GNU software (gcc, gas, ld, etc…), parts are covered by the standard X11 license, some of it is public domain, some of it was written by Cygnus and placed under the GPL.
Site: http://cygwin.com
