Ah, that brings back memories. I was using Intel iRMX on a commercial system in the mid 80s, and wanted to write a multitasking program on my IBM XT.

So I wrote a pre-emptive multitasking iRMX clone in C and a bit of assembler. Ended up using it to develop a mildly successful POS system running on a single PC with several VT100 terminals attached.