https://aantron.github.io/dream/, which is new and used by ocaml.org as well as OP

> No serious IDE, except emacs

and vim, and visual studio, and whatever else supports the LSP protocol via https://github.com/ocaml/ocaml-lsp

> The standard library was so lacking that there is at least an alternative.

While janestreet does have an publish their own stdlib, I personally try to stick to the stdlib whenever possible. Not to knock janestreet. I'm glad they're around and have contributed a bunch.

But overall I agree with you. It's been my favorite language to write in for years now. You can't just reach for off-the-shelf libraries for every little thing. Although the ones that do exist tend to be written halfway decently.