I still work with Meditech Magic, which is derived from MUMPS. Meditech was founded by Neil Pappalardo, the original developer of MUMPS. A strange system for sure, but it is incredibly fast and reliable. Since the early 2000s it has run on top of Windows Server, and uses a proprietary terminal emulator and encrypted telnet for establishing connections to the system. Magic has long been eclipsed by their newer 3-tier and web platforms, though there's still lots of Magic installations still out there.