Erlang, Elixir, Ada, plenty of others. Erlang and Ada predate Go by several decades, too.

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.