- The Reason syntax at https://github.com/facebook/reason
- Esy, the npm-like Opam-compatible package manager at https://esy.sh/
- Reason native tooling in https://reason-native.com/
- Not forgetting that Dune and Odoc, two standard tools in the OCaml ecosystem, both support Reason syntax.
EDIT: and I forgot about the various editor plugins which provide Reason support, the most well-known is probably https://marketplace.visualstudio.com/items?itemName=jaredly....