Not DOS but we recently had to virtualise a Windows XP box as it was running crucial software for a visitor attraction. The software was written by a member of staff who sadly passed away and the PC it was running on was approximately 20 years old.

We managed to virtualise it and then run it in a VM, and it needed a couple of USB-to-serial adapters passing through as well.

We're also finding some kiosks are running Shockwave Flash apps provided by companies that are no longer trading. We can decompile the files to extract the assets but at some point it's easier to just replace completely.