I believe it’s the only system you know. But it’s far from the only one.
I'd love to see a list of these, with any references you can provide.
You wanted sources, here's the chapter on tasks and synchronization in the Ada LRM: http://www.ada-auth.org/standards/22rm/html/RM-9.html
For Erlang and Elixir, concurrent programming is pretty much their thing so grab any book or tutorial on them and you'll be introduced to how they handle it.
In Go's category, there's Java, Haskell, OCaml, Julia, Nim, Crystal, Pony...
Dynamic languages are more likely to have green threads but aren't Go replacements.
You list three that don't, and then you go on to list seven languages that do.
Yes, not many languages support concurrency like Go does...
Source: spent the last few weeks at work replacing a Go program with an Elixir one instead.
I'd use Go again (without question) but it is not a panacea. It should be the default choice for CLI utilities and many servers, but the notion that it is the only usable language with something approximating CSP is idiotic.
So it's really Go vs. Java, or you can take a performance hit and use Erlang (valid choice for some tasks but not all), or take a chance on a novel paradigm/unsupported language.
That's 6 languages, a non-exhaustive list of them, that are either properly mainstream and more popular than Go or at least well-known and easy to obtain and get started with. All of which have concurrency baked in and well-supported (unlike, say, C).
EDIT: And one more thing, all but Elixir are older than Go, though Clojure only slightly. So prior art was there to learn from.