Microsoft open-sources MSDOS

https://github.com/microsoft/ms-dos

1.25 and 2.0, not very useful.

The 3.x and 6.x sources you can find leaked elsewhere, however...

>>2
That's what they did with VScode, put it on GitHub (which they own now) complete with all the telemetry crap.

You can also build your own XP/2k3 with the leaked kernel source that's also floating around out there.