Really loving Crystal, although not using it for any commercial applications (yet). It's really nice for building small command line apps. It has stolen my heart from Go TBH.
Suuuuper fast! (Not that it matters but likely faster than Go[0]).
Single binary builds/deployments (Just like Go).
[0] http://blog.seraum.com/crystal-lang-vs-nodejs-vs-golang-vs-h...
I might be one of the few people who would prefer Crystal remain single threaded and that effort go elsewhere in the language.