If the day ever comes that I end up in possession of a healthy late 20th century laptop, I'd genuinely consider putting FreeDOS on it. Not least because I threw away my customised MS-DOS 6.22 and Windows 3.11 floppies years ago (a regrettable decision).

For later hardware, I think I'll stick with Linux.

For a middle ground, I seem to remember Puppy Linux, which is designed to run on more limited hardware, runs most things as root. (Though maybe they've changed that in the intervening years. Correction welcome).