Keyhut POS: Free Point-of-Sale Software for DOS
You could probably get this running in a browser via emulation with one of those JavaScript DOS clones.From there, you could wrap it in an Electron window and write some nodejs glue code to let it interface with hardware and the file system.That would make it possible to rig up some kind of cloud storage for the database files and maybe start to think about getting it running on phones with React Native.You could sell the iOS app for a small price like $20, or a subscription model with in app purchases. That would help to fund a redesign of the website to a more modern single page app approach.