Cygwin is a free and open-source software development environment for Microsoft Windows. It consists of two parts: a DLL (cygwin1.dll) that acts as a Linux API emulation layer providing substantial Linux API functionality, and an extensive collection of tools, libraries, and documentation. Cygwin provides native integration of Windows-based applications, data, and other system resources with applications, tools, and data of the Unix-like environment. Thus it is possible to launch Windows applications from the Cygwin environment, as well as to use Cygwin tools and POSIX applications within the Windows operating system.