In addition to the one yawaramin linked, here are a couple of other useful related posts for interested readers, including yours from the Rescript forum as well (I think it fits here too):
- GoLang backend for ReScript? - ReScript Forum
- Best approach at implementing custom backends for OCaml in 2020
- What will be required to transpile OCaml to Lua?
Edit: it would be cool to see rehp revived…Compile to all the things!