> In the language and/or the standard library?

In Rust, we have extremely strong concurrency support in the language/standard library in the form of our type system, which disallows data races at compile time. We only provide 1:1 threading, but libraries can use this type system to extend it: there's N:M threading libraries, as well as more exotic concurrency stuff than we provide directly. Rust also generally takes a "no batteries included" approach, generally speaking.

In Ruby, there's Thread and Fiber. MRI's GIL hurts it here, but other implementations don't have this problem.