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).