In researching some information I was asked for, I came across a free operating system based - not upon Unix or Linux - but upon the Windows NT kernel. The NT kernel is the basis of Windows NT4, Windows 2000, XP and Vista.
The React OS can be found here, and is a free download. Mind you, the warning is that since it is still in development, it is not to be used for any stable and/or main PCs.
Being based upon NT, it means that a lot of drivers (and therefore hardware) and software for Windows will work under React OS.
I can't wait to try it out. (^_^)
