Roughly, Reason is OCaml, Derw is more like Haskell/Elm. Derw wears the Elm influence proudly, with similar design decisions and goals, and similar standards fo

Roughly, Reason is OCaml, Derw is more like Haskell/Elm. Derw wears the Elm influence proudly, with similar design decisions and goals, and similar standards for tooling. Reason is maybe more appealing to people from JS or OCaml backgrounds, with support for things like JSX. Derw is like Elm: functions and values.