Did an experiment last night.
Tried compiling Vault-OS with gcc and it sailed through no problems.
Ran under a 2 meg installation of MuLinux which itself was installed on UMSDOS in a FreeDOS partition.
Ran good, too. Ran amazingly well. Lightning fast.
My biggest heartache is that I never got PHP to run as CGI under DOS. I spent a good two weeks back in 2009 trying to compile it with Causeway-32 and could not get several libraries adapted to that environment.
So if I could get PHP to run as CGI on MuLinux, "technically" I would have a DOS based version of PHP. In fact, if I could get FastCGI to run PHP on MuLinux, I would have a modern CGI scripting tool running with similar speed to all my hardcoded in-memory CGI that runs now. That means I would spend a lot less time hardcoding web pages for things like inventory and other complex web apps and could do them in the far more dev friendly PHP. PHP even supports front-end client apps with PHP-GTK add-on package.
The reason this would be fantastic is that I use PHP all the time and have been coding with it for years. It is a powerful language embedded for a lot of reasons, including libraries available that put Lua to shame. I was never able to get it running on DOS but MuLinux is almost DOS with a Unix OS.
I have spent quite a bit of time making all my code cross-platform with batch files targeting x86, Win-32 and Linux environments and it looks like that will work out good because I may start developing this primarily on the machine with gcc from now on.
One really cool thing I noticed on Mu-Linux are truly retro looking interfaces for X-Windows, including monochrome. If you plugged this 16 color VGA into one of my black&white monitors (I bought several of these powered by 12 volt, 0.5 amps) it would look pretty awesome and definitely have a Fallout-flavor to it. Looks decent even at 320x240 resolution. Nobody else worries about these things but I often ask ... would this look okay if all you had was an analog television or 12 volt CCD monitor to run it on? I'm just trying to think of all the situations you might need to use it with the most barebones equipment imaginable you might scavenge from somewhere. I try to imagine how even people with not much experience at installation or configuration could still keep Vault-OS running no matter what and have it be very, very useful to them.
One of the reasons I am trying to remove emphasis on the Windows port is that I now have enough experience with Windows since 1989 to know there is no way in hell I want that running my system post-apocalypse. I would describe it as the OS destined to fail you when you need it most.