NT kernel supports multiple OS flavors
Interesting with all the comments suggesting various UNIX emulation layers as to cater for BASH users.
Back in the 90's NT was heralded as being able to support different OS subsystems, Win32, OS2 and Posix programmes. While Win32 of course was the dominant one and OS2 went to oblivion the Posix subsystem actually lingered on for quite some time as subsystem for UNIX (SFU on Windows XP and SUA on later Windows versions). Interix was the company that provided GNU tools and compilers for free until a few years ago.
If Microsoft had wanted to persuade UNIX fans to use Windows, SUA could have been a huge boon had they not rather sadly decided to kill off the Posix subsystem in Windows altogether. It is still present in Windows 7 Ultimate. On Windows 8 it is only present in enterprise version but marked as deprecated. Granted, the integration with the rest of the OS was far from perfect and always had the taste of being an alpha-version. It wasn't a stable environment on which to run production tools and the GNU compiler never went beyond version 3.3 since Microsoft never got around to commit their amendments to the compiler source code to the Free Software Foundation. Likewise the integration with the rest of the OS like the Windows desktop was flaky, inconsistent and unstable.
In spite of all this SUA may still be an alternative if you have a Windows7 Ultimate PC for work and want to use BASH.