Is there a niche that OCaml fits really well with few packages needed? For example: Go has a great stdlib for networking (servers, etc); Rust is pretty good for CLI tools.
I've used OCaml for writing small compilers and it was really clean but that's a toy thing that will not see much real world usage.
Compilers, provers and static analysers. It's awesome for that. That's what the language was built for initialy: developing the Rocq prover.
It's surprisingly nice for web development also when you compile to JS. The ecosystem around Mirage and microkernel is quite impressive and if you want to build low level things and I for one like it significantly more than Rust for CLI tools.
It's a very versatile language honestly. It's opinionated enough that you have a clear idea of what would be the community choice but not so much that you can't just go to town with a different solution if it suits how you want to approach the problem more even it is an imperative implementation or even something object oriented.
I personally view Ocaml as basically a better Python with more features, better performance but without the huge success.
I've used OCaml for writing small compilers and it was really clean but that's a toy thing that will not see much real world usage.