I invented a pretty strange language, actually. Back in my undergrad.
It's a declarative language where the input to every function is a "table", and the output of the function is some disjoint assignment of "rows" to categories, described by a predicate, or an exception if no assignment is possible. For example, if you wanted a function that takes a set of numbers, and returns two disjoint subsets, the first containing 10 numbers between 1 and 10, and the second containing 10 numbers between 5 and 8 (yes the ranges overlap), that would be a 3-liner in this language: one line for the function signature, and one line for each of the predicates (I was going through a Python phase).
Of course it wasn't limited to numbers; the tables could have arbitrary fields (and a single 'quantity' field). The predicates could key off of any combination of fields as long as the categories they described were disjoint or proper subsets of all of the other categories. Normally something like this would involve integer linear programming, but because it was limited in this way I was able to find a reduction to network max flow, so my solver would always run in polynomial time.
It's generally useful for resource allocation type problems where you have a large number of heterogeneous "things" and you're trying to assign them to designated roles. Like for a more practical example, if you had a million soldiers, 700k have marksmanship training, 400k of them have medic training, 300k of them have engineer training, and 100k of them are officers. Not everybody can do every job, but you've got enough overlap to make things confusing. If you actually need 400k marksmen, 40k marksman officers, 400k medics, 10k medic officers, 200k engineers and 30k engineer officers, all working at those roles full-time, this language will let you concisely define the proble, and the solver will efficiently tell you exactly how to divide up your forces (if possible).
It's the kind of language that I'm sure some rich company working in some obscure domain would literally kill to have, but I've got no ****ing clue who that'd be.
