Yes, Crystal is pretty cool. Though I have found that it is hard to compile for different platforms. If you need speed and concurrency, giving jruby a shot is worth a try. It speeds up your code through both being fast and having 'real' concurrency.
However, doing CLIs or binaries for whatever reason, then it wouldn't be so neat. Ruby wouldn't either, but GraalVM might be able to provide something good for it in the future as well.