I've primarily been a one-trick pony for years on the server-side with Ruby, but I'm curious what languages other folks are using on the server-side for production apps.<p>What are you using to complement Ruby in production?
Elixir. Why? Because it has tooling that is up to the high standards you're used to using in Ruby and Rails. It has a great ecosystem, package manager, and build tooling. The documentation is fantastic and filled with examples. It also has type annotation and type checking and being built on top of the Erlang VM its really good at soft realtime apps which is probably most of what you're doing server-side anyway.<p>I've used other languages mentioned by others here in projects (Go, Clojure, Haskell, Rust) and although many are nice, for instance Rust has many excellent features and a sophisticated build and package management tool to go along with it, and Go can be somewhat useful if you want a UTF8-friendly concurrent and GC'd C, I still don't think they're good fits for the majority of server-side apps.
My favorite language, it's the best, trust me!<p>More seriously: what are your goals in learning a new language? If it's new skills or ways of thinking, go for something that's quite different from Ruby in some <i>educational</i> way. Clojure, Elixir or Haskell will teach you rather more than Go will, each in their own way.<p>* All three are functional, so no mutability by default.<p>* Clojure has software transactional memory (as does Haskell, I believe?), and it's a Lisp so you can create macros and customize the language.<p>* Haskell has a very powerful type system.<p>* Elixir use Erlang's agent-based runtime and functionality, which e.g. lets you do hotswapped code upgrades on a running server.<p>Go has a stupid type system (e.g. Java's is much better) and a concurrency system that doesn't help with any of the hard problems in concurrency. On the other hand, Go might be a more marketable skill than any of the ones I recommended for educational purposes.<p>So it depends on your goals.<p>More ideas on choosing which technology to learn more broadly: <a href="https://codewithoutrules.com/2016/04/27/which-technology/" rel="nofollow">https://codewithoutrules.com/2016/04/27/which-technology/</a>