Well, that's a big assumption and rude at the same time. I post a lot here about the history of operating systems. I'm well aware of DOS and CP/M. I know little to nothing about Concurrent DOS or FlexOS because of no need. So, let's look at your link:
"IBM licensed Digital Research's real-time OS, FlexOS, for its point-of-sale machines."
...the article you link says "IBM originally chose DR Concurrent DOS 286 as the basis of their IBM 4680 computer for IBM Plant System products and Point-of-Sale terminals..." The original source I read those terminals said they were based on Concurrent DOS. So does my comment and this link. Clearly, I did some research. Kroger's POS's also said IBM 4680.
Let's see where FlexOS comes in: "IBM announced the adoption of FlexOS... as the basis of their IBM 4690 OS..." Ok, FlexOS was used for a different one I didn't look up because Kroger didn't use it.
So, you're saying I'm ignorant about OS's because I didn't study a proprietary OS (FlexOS) I've never seen, the local store didn't use, and that was likely inferior to most RTOS's I know of? I'm not sure what your aim was.
I think you really do not know much about the history of PC operating systems.
IBM licensed Digital Research's real-time OS, FlexOS, for its point-of-sale machines.
https://en.wikipedia.org/wiki/FlexOS
FlexOS is related to DR's Concurrent DOS:
https://en.wikipedia.org/wiki/Multiuser_DOS
... which was the descendant of Concurrent CP/M, which was the offspring of CP/M-86, one of the 3 original OSes at launch for the IBM PC in 1981 (along with PC DOS and the UCSD p-System).
CP/M was the original industry-standard OS for 8080 micros. It is what MS-DOS is a knock-off version of -- MS-DOS was licensed from SCP, whose QDOS was a copy of CP/M.
"Some group tried," indeed. This is the original OS company, successfully trading and dominating the industry when Bill Gates and Paul Allen founded Micro-Soft.