There are many thousands of DOS programs still in active use today -- and not just by hobbyists or for educational purposes, in active commercial use, if you require economically productive criteria to consider something practical: Many industrial control systems still used every day operate through DOS applications written in the 1980s.
Spending a lot of time and money on a complete rewrite upgrade to make these control systems to use some other OS 'just because' would serve no practical purpose. They work fine on DOS. It would be expensive and risky to change that.
At the same time, MS-DOS has been unmaintained for decades. FreeDOS is almost entirely compatible with MS-DOS applications, and is still actively maintained with bugfixes and so on.
FreeDOS sounds like a very practical option indeed.
If the control systems have hard real-time requirements, FreeDOS may be one of the few options. (At least I assume FreeDOS is, since MS-DOS was.) Presumably it's a lot cheaper than QNX, too.
Spending a lot of time and money on a complete rewrite upgrade to make these control systems to use some other OS 'just because' would serve no practical purpose. They work fine on DOS. It would be expensive and risky to change that.
At the same time, MS-DOS has been unmaintained for decades. FreeDOS is almost entirely compatible with MS-DOS applications, and is still actively maintained with bugfixes and so on.
FreeDOS sounds like a very practical option indeed.