[skissane]

For DOS, I believe the core was only ever Microsoft or IBM. Some DOS versions bundled add-ons by third parties, but they are hardly essential for operation - e.g. MS-DOS 6 included DEFRAG and MSBACKUP (both licensed from Symantec) and MSAV (licensed from Central Point Software)

Similarly, with Windows, the third-party components are generally inessentials such as certain device drivers, games, some optional system components like the ZIP file support in Windows Explorer-you would still have a usable OS with these bits ripped out. Parts of NTVDM are third-party licensed, although I believe that’s mainly the software CPU emulator used on RISC platforms, I think x86 was mostly Microsoft’s own code

[lproven]

Agreed.

From MS-DOS 6, remove the defrag, backup and antivirus programs, and DoubleSpace/DriveSpace, and that should I think cover all external code.

If I remember correctly, it didn't include CD-ROM drivers, just MSCDEX to run on top of one... and the network stack was an optional extra. I'm not even 100% sure it includes a mouse driver as standard.

IBM PC DOS 6.3, 7.0 and 7.1 include some additional IBM code: Rexx in place of QBASIC, the IBM E editor, but not much else.

[rezonant]

Isn't the zip support in explorer the stuff written by Dave Plummer? I would imagine MS has the rights to that already, and if they don't, I'd imagine Dave would, and I'm sure he'd be fine with it being released.

He has lots of YouTube videos about the zip stuff.

[nar001]

It was but Dave sold it to MS, so they own it

[chucky]

Yeah, but it's the "mostly" and "I think" that will cause lawyers to start sweating and force someone to do a bigger and more expensive investigation.

[lproven]

DOS is relatively speaking tiny and actually pretty modular. You can delete a handful of files, mostly binaries and some help files, and that's it, code gone.

From the source it's a little different but there's little integration between the bits.