I've been messing around with Perl 6 again lately, just because I'm interested in the built-in set operations.

It's concurrency features are clearly very advanced, and it'd be on my list of contenders for those kind of applications. I'd actually like to see a serious comparison between it and, say, Go and Elixir/Erlang to see how it stacks up on ease of use (and how big the performance penalty is at the moment...).