It's a family business, and the software works really well (a medical niche), so the investment to update the stack doesn't make any sense. (And there's no need to bother clinicians neither with things that don't add value) I have a VM for tweaking and working with it. I have multiple ETL scripts that extract the data to a modern ERP.
I don't have access to the source code, but I have tried to reverse engineer it from multiple angles. Essentially it's a 16 Bits client written on Delphi with a database (dBase) that doesn't support multiple readers or writers, shared via a network drive. Clients read files from the shared drive and create locks to avoid multiple clients working in the same data. That's the main source of pain, but the clinicians adapt to it in a week or so.
I haven't seen yet a modern system as complete as this one. There are multiple clinical centers in the area using the same software (25ish) and the 2-3 that moved into newer systems regretted greatly.
The market is too small for any new developments. But the guy who built it in the 90's maintains it and earns enough to live happily.