GNU BASH is a shell which is modelled after the original Bourne shell, and is installed as the default shell upon most installations of GNU/Linux.
This page allows you to download a precompiled copy of GNU Bash v2.03 for Microsoft Windows platforms:
The archive contains the complete source code too.
Note: I offer no support for this program. You might prefer a more recent version of zsh available from the unix-utils collection project - or bash 3.x from the Msys tools collection.