It is (or was) a real time protected mode OS for 286 processors.

I actually used that compiler over 25 years ago, it generates Intel OMF files with 8086/80186/80286 - As I recall one can select the target.

So post compiling, one should be able to link the result to target a DOS machine, VM, or even Dosbox.

I'd suggest porting it, but rather simply simulating the FlexOS SVCs, since it doesn't really need any of the RT capabilities, merely the file access, memory allocation / free, and possibly execution (COMMAND SVC).

The package contains two forms of the compiler, a single executable version, and an overlaid version. The non overlaid version would be easiest to get working in such a simulated approach, as one would not have to implement the OVERLAY SVC.