Quoting from Jim Hall's "FreeDOS turns 25 years old: An origin story":
Around 1994, Microsoft announced that its next planned version of Windows would do away with MS-DOS. But I liked DOS. Even though I had started migrating to Linux, I still booted into MS-DOS to run applications that Linux didn't have yet.
Given that DOS had useful software not available for Linux, it seems like there might might have been a market for software that would enable at least some DOS software to run natively on Linux or another UNIX derivative. Obviously software that directly accessed the hardware would likely misbehave in such an environment, but as evidenced by the existence of machines like Siemens PC-D, there was at least theoretically a market for systems that could only run "clean DOS applications".
Windows 2000 (and possibly earlier versions of Windows NT?) had a similar compatibility layer, NTVDM, so theoretically a compatibility layer like this may have been able to exist for a UNIX-based system similar to how Wine works today to allow Windows applications to run on Linux. And Intel-based CPUs at the time supported a virtual 8086 mode that would have allowed 16-bit real-mode code to run in a virtual machine under a 32-bit UNIX implementation (assuming the OS was running on an Intel-based CPU of course).
A system like this could have theoretically appealed to power users of UNIX-based systems, since it would have allowed multiple MS-DOS applications to run simultaneously and possibly even be integrated into shell scripts depending on the features of the DOS compatibility layer.
Did DOS compatibility layers like this exist for UNIX or any UNIX-like OS? To be clear, I don't mean DOS emulators like DOSBox — the age of hardware I'm thinking of would likely have made the performance of a full system emulator horribly bad, even for DOS. I mean something closer to Wine or NTVDM.