Libraries
Reason libraries are just like OCaml libraries: hosted on opam. Here's a list of packages published by on the opam repository written in Reason: https://ocaml.org/p/reason/latest#used-by
Historically you can find some libraries on npm as well, since previously Reason and BuckleScript (now ReScript), but we're moving away from that. The npm packages are mostly outdated and might reference parts of Reason that aren't correct anymore. The main motiv is that we want to focus on the opam ecosystem, which is the standard for OCaml libraries, ppxs and tools.