Flirting with Crystal, a Rubyist Perspective

Quick summary:

Although Crystal is single threaded, it implements the reactor pattern (like Node.js), so it can be useful to build highly concurrent applications with the advantage that appears to be faster that Node.js (small benchmarks) and has a nicer syntax than JS, Go or Rust.

Crystal's aim is not being a faster fully compatible Ruby runtime, it just wants to leverage Ruby's nice syntax and standard lib in its own world. It does not support any idea of reflection and consequently meta-programming, but with Macros (and more effort), you could go somewhat close to it.

Also, if you are not interested in replacing Ruby with Crystal completely, you could just use it for some CPU intensive code, writing almost the same Ruby code but as a compiled native extension.

Crystal does not support Windows yet.