I feel that I've been procrastinating a lot in my free time and it's time to learn something new.
I see the hype around Go and Rust and I believe I'm missing a lot in my professional development. I'm involved with my start-up and I am facing a lot of challenging data analytics and software development problems during the day. I am using Java/JavaScript/R on a daily basis, but these are mature languages that have been around for a while and I have a hard time learning new frameworks that are beyond my work scope.
So what (hot) languages/frameworks are you learnin/using now, that give you the warm feeling that you get a lot of useful knowledge out of them, that's widely applicable?
Elixir is a really cool language, and also a great way to learn functional programming. But more than that, it gets all the non-languagy stuff right. The build system is amazing, your code hot-reloads out of the box, dependency management is very well done (source-only, git-friendly, project-local, etc), the community is very friendly and going fast.
And code scales by default. I might exaggerate here, but sometimes it feels like need to really try to write code that's hard to spread across servers. If you consider it's non-trivial to even use all your CPU cores on Node.js, the Erlang VM will blow your mind.