It's especially relevant in PL or Databases. DB2 did such foundational work in database theory, and Python 3.6's new dicts finally made some very simple database theory finally available to users.

In PL, there's a massive amount of awesome languages that pretty much existed for the purpose of writing a PhD or doing something funky with semantics. It takes /really really/ long to get into an industrial strength language. Look at Rust for example, it's the first incidence of real Algebraic types for a non-gc language (excluding C++), letting you do wonderful things like https://github.com/lloydmeta/frunk

Some of my favorites are

http://bloom-lang.net/

https://www.luna-lang.org/

https://www.propellerheads.com/en/reason (i contend it's a fantastic programming language for the task)

https://cseweb.ucsd.edu/~wgg/CSE131B/oberon2.htm