Well for example, one of the most interesting applications of OCaml in finance (well, fintech) is implemented in OCaml and open source: https://gitlab.com/tezos/tezos

Then there's Bloomberg: https://ocaml.org/learn/companies.html

> Bloomberg employs OCaml in a advanced financial derivatives risk management application

Press release from Bloomberg announcing BuckleScript: https://www.bloomberg.com/company/press/open-source-at-bloom...

> We are not currently using BuckleScript on the Terminal, but stay tuned…

This seems to suggest that they were looking at programming Bloomberg terminal applications in BuckleScript, compiled to JavaScript, at least at one point.

There's also LexiFi: https://www.quora.com/Is-the-OCaml-language-used-in-quantita...

I think if you go looking, it's not hard to find OCaml in finance in certain niches.