The last 'pure' MS-DOS was v6.22. With the introduction of Windows 95 and thereafter, Microsoft would have you believe that DOS was dead. However DOS was still alive and kicking in its 'version 7' incarnation, running things behind the scenes for Windows 9x and ME.
Although Windows NT and anything after Windows 2000 did not run on MS-DOS, there is a DOS emulator known as the Command Prompt, which does most things the original DOS used to. It's a very powerful tool too, if you know how to use it.
DOS for DOS' sake
DOS on a USB Poo Stick