Cygwin – a distribution of popular GNU and other Open Source tools running on Microsoft Windows. The core part is the Cygwin library which provides the POSIX system calls and environment these programs expect.
The Cygwin distribution contains thousands of packages from the Open Source world including most GNU tools, many BSD tools, an X server and a full set of X applications. If you’re a developer you will find tools, headers and libraries allowing to write Windows console or GUI applications that make use of significant parts of the POSIX API. Cygwin allows easy porting of many Unix programs without the need for extensive changes to the source code. This includes configuring and building most of the available GNU or BSD software, including the packages included with the Cygwin distribution themselves. They can be used from one of the provided Unix shells like bash, tcsh or zsh.
Cygwin/X is a port of the X Window System to the Cygwin API layer for the Microsoft Windows family of operating systems. Cygwin provides a UNIX-like API, thereby minimizing the amount of porting required.
Cygwin/X consists of an X server, X libraries, and nearly all of the standard X clients, such as xterm, xhost, xdpyinfo, xclock, xeyes, etc. Many more X programs are also packaged for Cygwin. See also the features and screenshots pages.
Cygwin/X is licensed under a MIT/X11 style license. Cygwin is licensed under a modified GNU General Public License that specifically allows libcygwin.a to be linked to programs that are licensed under an Open Source Definition compliant license without such linking requiring that those Open Source programs be licensed under the GNU General Public License .