I recently discovered it. It's pretty amazing for how incredibly easy it is to build distributed applications with it, that is the part which impressed me the most. It handles concurrency well for sure but same program seamlessly across multiple computers is just awesome. I know it's basically just taking this functionality from being built on top of erlang already but it's still very impressive. Plus like crystal if you already know ruby, having tried to base it's syntax on it, it's an easy thing to pick up if you can grasp the functional aspects too.