But that's the thing: places which fit those requirements usually run some IBM solution (AS/400 and the likes). I've never encountered VMS in production before, so I'm really curious to some concrete examples of companies using it.
I used to work as a software developer in the UK insurance industry, and I can tell you that we (and hence several of the insurers/brokers we dealt with) used OpenVMS.
In contrast to some of the other comments here, we weren't using it because moving to another OS - or architecture - would have been a pain. In fact, our software originally ran on x86 machines at some point in the distant past, before we migrated it to OpenVMS relatively recently.
I don't know why OpenVMS was given preference over GNU/Linux, *BSD, or Windows; I'm guessing that the technical managers above me had their reasons, but I couldn't say what they were.
I left that job a few years ago, but I think that they did intend to eventually phase out the VMS systems as our new, GUI-based product slowly replaced the older text-based one.
We use it at our company (financial software). One of the reasons being that the code is older than Linux and VMS was a good bet at the time.
We have almost entirely moved away from it and onto Linux but considering the decades of code and systems built on and around it, it is truly a monumental task to move off VMS while keeping a system used by very high paying clients running smoothly.
I haven't used other mainframe solutions, but one of my favorite features of VMS is logicals. Logicals are environment variables backed by a clustered key value store that's safe to use for distributed locks. Logicals appear to your process in a hierarchy of tables that inherit from one another, by default you have: job (shell subprocess) > process (shell session) > user > group > system (node) > cluster. You can also build your own tables stored with which ever chosen locality (system, cluster, etc) in the hierarchy. Meaning if you follow "12-factor" design, well it didn't have fancy name then, you could do things change configuration cluster wide in an instant.
We used to have a CNC machine controlled by a VMS box. I almost burst into tears when it was unceremoniously decommissioned while I was on holiday - that thing had been up for more than six years! (Which is not at all uncommon in VMS circles!)
