My first job was supporting a custom application running in UniVerse on Solaris. It originally ran on a Prime mainframe and UniVerse was one of the ways you could run this type of software on a modern system. I really enjoyed working in the Pick MultiValue environment. In many ways, this was a NoSQL database from before NoSQL was a big thing.
I don't work in this world anymore, but I've been playing with ScarletDME (a fork of OpenQM, another MultiValue database, from before they closed the source) and seriously enjoying it.
As a result of this first job I've got a special place for "old" programming languages/environments. My dream retirement job is to work for either the CRA or IRS supporting their old systems. Between the complexities of income tax and the old-school code that can never be retired I think I'd love it.