Cygwin

Cygwin is a collection of GNU and Open Source tools that brings functionality similar to a Linux distribution to Windows, paired with cygwin1.dll, a DLL providing substantial POSIX API functionality. It is not a way to run native Linux apps on Windows; applications must be rebuilt from source to run on Windows using Cygwin, and native Windows apps do not automatically gain UNIX functionality such as signals and ptys.

The project is installed and updated through the Cygwin Installer, which handles fresh installs and updates of an existing installation. Individual packages in the distribution are updated separately from the DLL, so the DLL version does not serve as a general distribution release number. The current Cygwin DLL works with recent commercially released x86_64 versions of Windows starting with Windows 8.1, while older systems are covered by earlier versions and the Cygwin Time Machine. Support resources include a FAQ, User's Guide, API Reference, mailing lists, newsgroups, and IRC channels. The DLL and utilities are distributed under Cygwin authors' copyright, with other packages carrying their own copyrights.