Unfortunately Rune and Dyon[0] are dynamically typed, which isn't so attractive to me.
More promising are Gluon and Mun, both of which are statically typed. Of these two, Gluon has a somewhat alien syntax if you're coming from Rust (it notes it's inspired by Lua, OCaml and Haskell) so Mun is probably a better choice...but it seems very early, and the website notes as much (to serve the needs of a Rust-scripting-language I'd want seamless interop between it and Rust, which isn't quite there).
So I don't think there's anything in this space right now, but there are some promising options.
If you're wiling to go a little further afield, I'm kind interested in assemblyscript[3] - it's 'just' another WASM-based language so it's not a huge leap of imagination to believe there could be tooling to enable the seamless Rust interop. Just a matter of effort!
[0] https://github.com/PistonDevelopers/dyon [1] https://github.com/gluon-lang/gluon [2] https://github.com/mun-lang/mun [3] https://www.assemblyscript.org/