There is the small standard library that ships with the compiler. And then there are more extensive ones such as Batteries and Core. It is easy to generate docs in Reason syntax from OCaml projects using `redoc` tool. Here is Reason docs for:

- OCaml compiler's stdlib: http://kcsrk.info/reason_stdlib_docs/index.html

- Batteries: http://kcsrk.info/reason_batteries_docs/index.html