MUMPS

MUMPS (aka M) was actually my first professional programming language at Epic Systems, the tech giant of the Healthcare space. It’s contemporary with C (which is also still used), and has several features which were unheard of at the time.

1. M bundles a reasonably efficient database with the language itself. Every variable supports jagged hierarchical arrays (which we usually call objects in other languages). These were implemented as balanced binary search trees, which means it’s difficult to write slow operations (at the cost of slightly sub-optimal performance for everything).

2. M was designed for massive server/client operations, handling concurrent use and access by tens of thousands of users out of the box.

3. M was incredibly terse. We laugh about the horror stories now, but when it was developed, every byte mattered, so single letter keywords and white-space-award syntax were features, not bugs.

As a result of these strengths, M solved real problems for large organization, managing data and concurrency at scale, with a simple storage paradigm that prioritizes good enough performance all of the time.

M does the "noSQL" or "multi-model" or "hierarchical" or whatever they want to call it database as good or better than many a dedicated noSQL engine written by kids who weren't even born when MUMPS started. Which is no wonder -- it has been optimized for 50+ years. And it gives you a reasonably complete (if not very readable) language optimized for working with that database. It also gives you some nice ways to shoot yourself in the foot by allowing EVAL-like things and modifying code on the fly...

It is also well-entrenched in many areas where NOT breaking things is far more important than moving fast (healthcare, finance).