2.6 Microsoft Windows
In 1995, Microsoft released Windows 95, which soon became the most widely-used operating system in the world. Autoconf and Libtool were written to support portability across Unix variants, but they provided a framework to support portability to Windows as well. This made it possible for a program to support both Unix and Windows from a single source code base.
The key requirement of both Autoconf and Libtool was the Unix shell. The GNU bash shell was ported to Windows as part of the Cygwin project, which was originally written by Steve Chamberlain. The Cygwin project implements the basic Unix API in Windows, making it possible to port Unix programs directly.
Once the shell and the Unix