As much as DOS allowed multiple processes, even if only one was executed at the time and there was no multitasking outside of ill-fated MS-DOS 4.0 and various Concurrent DOS products.
You were not there. Multitasking? Xenix.
Multitasking DOS? DOS Merge.
Pre-emptive multitasking? AmigaOS.
DOS 4.0M was task switching.
OS/2 2.0? I'm being extremely facetious.
Give me a date, and I will tell you what existed.
Nothing mainstream existed until windows 3.1. at least on x86/32
There also was OLEC on windows 2, that did run in real mode, but the only thing that took advantage of it was the demos, and samples: no commercial product used it.
DOS still allowed you to run child processes, and TSRs were a thing that sometimes caused funny behaviours.
My point was that running your own chosen process as PID1 (or, to be more practical, a minimal init or maybe system v init with single entry for process to run) matches the requirements of running small set of processes just as well as DOS (if you need more, it's IMO more worthwhile to start getting a build of some RTOS for your platform)
