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A lot of OCaml, but also some Rust, Cobol, Solidity, and a lot of Formal Verification! OCamlPro is always looking for skilled OCaml developers to hire, so if you are interested, contact us at contact@ocamlpro.com
Who is the biggest Cobol user in France?
I remember this language from university, it was quite good to make text-driven interfaces.
I also wonder on which kind of computers it runs (old mainframes?).
It’s actually difficult to say who is the biggest user in France, as most companies do not communicate much on their use of COBOL… no need to explain why 
But you can check job offers to get an idea.
There are articles every year in the press, saying that COBOL is still in use and actually probably the most used language in number of running lines, though most of them have been written decades ago… Also, programmers tend to work by copy-pasting code, so the increase is even higher than for other languages…
COBOL is mostly used on Mainframes, old and new ones (IBM Z series mostly), but also on PCs, there are a few distributors of compilers for Linux, including GNUCobol, the only open-source one as far as I know.
The biggest user could be EDF, or SNCF, I guess.
Yes, I guess, banks and insurances are also big users in general.