Hey, I've also used and loved Orpie!

I'm not extremely familiar with any of the ML family, but Eric Lippert had a blog series I followed for a while in which he was writing a Z-Machine in OCaml: https://ericlippert.com/2016/02/01/west-of-house/ I followed along but in Rust for a while, though I think he paused the project at some point and I lost steam.

I learned more about Rust (which, IIRC was first implemented in OCaml) than I did about OCaml, but it's always seemed like a nice language.

Lippert started doing that blog series as part of his learning journey when he got hired at Facebook to write OCaml. Just a fun historical fact.