For a built-in reference semantics system that's finer-grained than Rust's, there's Pony's system (has a GC, but Orca is supposedly faster than C4 or HiPE/BEAM).
I’d love to use Pony (sans GC), but the project is dead, Sylvan has lost interest, Sebastian has lost interest, and even its biggest advocates (Sean and Joe) have moved on. It’s s shane since I really really like what Pony was doing.
The project is definitely not dead! Right now it is entirely volunteer-driven, so the amount of work being done depends on the amount of work put in by the overall community. Feel free to drop by our Zulip to catch up on the latest developments: https://ponylang.zulipchat.com/
https://tutorial.ponylang.io/reference-capabilities/capabili...