FFI support in Rebol originated with Rebol2's paid version, "Rebol/Command":

https://www.rebol.com/docs/library.html

It wasn't part of the Rebol3 open-source release, but Shixin Zeng of Atronix Engineering implemented a version of it, described in this 2019 video:

https://www.youtube.com/watch?v=fMeTqPyrNF4

That implementation was baked in to the core of Atronix/R3. This is a migration of that code out of the core, and into an extension for Ren-C.

Time available to support this code is limited, as it's not a key focus for the Ren-C roadmap. However, it's meant to be kept running as a useful and non-trivial example of the extension mechanism.

Almost always, a more rigorous form of interoperability can be achieved by building C code as an extension linked to the interpreter core. This provides more robust interaction than using brittle FFI calls from a GC-based language with unmanaged pointers. (This is true of basically every language's FFI.)

However, this means needing to have access to a compiler. If not using a compiler is desired, another simple way that frequently works for triggering "foreign" functionality is to use CALL to invoke a command-line program that can perform the needed action. It can then write any returned information to a file (or stdout).