Mastodawn

MS-DOS 4.0 is now open source under MIT licence.

The original sources of MS-DOS 1.25, 2.0, and 4.0 for reference purposes - microsoft/MS-DOS

GitHub

@sos Can't wait for the upcoming flood of new DOS-based operating systems!

2.0 was updated one month later, so suspect some things in there may not be fabulous.

Also, 4.0 is a dead end.

“For reference purposes”