I'll add Pony to the list. This language uses the actor model like Akka and Erlang, but allows for the safe sharing of data between actors enforced by an an ingenious use of the type system. The result is an actor programming model with better performance than Erlang because mutable data can be safely shared.

I have been a long time Java developer, and I have worked a lot with highly concurrent code. Pony really opened my eyes to what was possible.

Unfortunately, the language, standard library and runtime is still pretty immature. It does however have very good 'C' interop. So for some problems it would be a very good fit.

For Java at least, the Java Concurrency API is preferred.

Akka actor framework comes to mind. I am in the process of learning it and it is definitely simpler to wrap your head around it.

Actor model with Elixir/Erlang and the BEAM VM.