Progress Openedge.
I have never seen anyone on HN mentions it. The codebase is from the 90'.
before that, I have worked with a codebase from the 80s, 10 years older than me.
How do you find it? I had a colleague who had worked earlier in a company where they used it, IIRC as the language/4GL for work on MFG/PRO (a popular ERP package then). Think I remember him saying it was good (just Progress, it was called then).
Believe it or not, I actually deal with Progress too.