I’ve used the DOS build of OCaml! Back in 2000, in my freshman year at the uni, I was using a 486SX/33 with 4 MB RAM, dual-booting DOS / Monkey Linux. The latter didn’t support OCaml as it was libc5-based, so I had to resort to the DOS build. Used it for some Programming 101 assignments.
I also love getting old software working on DOS. I particularly like finding things which weren’t meant to work on DOS and get them going there. Roguelikes are good for this. There’s an old DOS version of SQLite going around, and it’s only mildly difficult to get more recent versions working too.
How about a MirageOS port to DOS?