So, I came across this project from some random google search on Watcom the other day. Simply put it is a MS-DOS API that is supported in both a 16bit real mode operating system, and a 32bit operating system. It is quite sparse but very interesting all the same. Using the ancient EMX port of GCC you can build 32bit (simple) programs, and run them in the 32bit DOS like Operating System. What makes this even more interesting is that there is a port to the IBM 370, and 390 based hardware, along with the fictional 380.
You can download my diskimages, (VMDK & floppy disk) that I’ve used with Qemu to build & boot PDOS both 16bit and 32bit.
The included libc & system libraries are lacking compared to real MS-DOS, but this is public domain code, and with a bit of TLC it could be made into something much more.