Rexx! Loved that on OS/2, pretty happy to see that it has a home on FreeDOS.

FreePascal & Lua! Thanks

One can use the free Open Watcom or DJGPP to code in C or C++.

Is DJGPP still maintained? All I could seem to find are very old versions, unless the project has moved somewhere that I couldn't find.

This website is such a blast from the past. I remember using DJGPP in highschool in 1998 and it still looks just the same. Glad to hear that it's still being used and updated; maybe I'll give it another try for old time's sake.

Check Open Watcom v2[1], which is still actively developed. Also the JWasm[2] - FOSS alternative to MASM.

[1] https://github.com/open-watcom/open-watcom-v2

[2] https://GitHub.com/JWasm/JWasm

I think LLVM is adding 16 bit support of some kind. It's not something that's "self-hosted" on DOS itself like some of the other solutions are, but the flip side is that this gives you a lot of flexibility. You could even develop in Rust.