I have some legacy software used by maybe 2 users that rely on a .net/fortran interface that most assuredly is long out of development. We have the development environment and source code for this rusting application backed up in a VM; so we can get back to it if for some reason we have to make a minor update to it.
It's obviously in need of a respec and redo, but, you know, usual cost/benefit nonsense, and who pays arguments.
There are some commercial packages out there with similar functionality; though black box is a major blocker. A Canadian offering we've tested in the past had some subtle, but detectable errors in the maths and so was not suitable for the fine margins we need... And having found "some" errors, it raises questions about what else is lurking. I'm aware of another outfit in Austria that have done a webapp with similar functionality and has a few users from other operators whose opinions I value, so there is probably something in it... But we do like having the source to interrogate.
I am fairly certain given the small user base however, that the parent org will do nothing until something breaks; which is par for the course.