There definitively are some third party components in Windows, but I believe in the core most is either written directly by MS or at least the copyrighted (or i

There definitively are some third party components in Windows, but I believe in the core most is either written directly by MS or at least the copyrighted (or its handling) is transferred to them. Parts of an old NT kernel has already been published for a limited audience (mostly education and research, with some additional prereq and with the need of an explicit licence), so probably it can be done again.