I've been working on JavaScript runner for untrusted code. The whole API is only exposed via messages passed over stdio. Security layers: V8 isolates, two-stage seccomp, frozen globals, mount namespaces, landlock, and more. https://github.com/jonathannen/hermit

Plus it's too early to really show, but also working on a dataflow language (w/ immutable data) that uses some code semantics from Rust/Zig and friends: https://github.com/jonathannen/badger