The OCaml runtime is very easy to embed, as runtimes go. We've got it compiling in Mirage as a standalone kernel, as a FreeBSD kernel module, and others have had it running on 8-bit PIC microcontrollers:
http://www.algo-prog.info/ocaml_for_pic/web/index.php?id=oca...A fun project that I discussed with the Rust devs at last year's OSCON would be to rewrite the OCaml GC in Rust. Get in touch with me if you're interested and want some guidance on how to go about this.
