OCaml as well-- the first place that comes to mind is Jane Street.
I've met a few devs from Jane Street - very nice people. Had the pleasure of meeting Yaron Minsky as well (he was a guest lecturer). Harvard had an entire intro course dedicated to OCaml...while it was a nice introduction to functional programming I can't say I've ever touched the language since...
The first and the only.
What about Ahrefs? Also, some people must be using Ocaml's cousin F#, or Jon Harrop would not have a job.
Edit: oh, finance. Right.
Last time I've checked, Harrop was everything but happy with the current F# situation (tooling, ecosystem, etc.)
In years of finance mostly involved in trading, exchanges, and risk - from prop firms to bulge bracket. I can count 3 times I've seen Erlang used. None of them have been major projects.
It is still overwhelmimgly dominated by C++ and core Java with some Python in there too.
I mean, that's three times more than I've seen it used. I'd wager that finance is a second only to telecoms when it comes to "industries that use Erlang".