Crystal programming language is super interesting. I've spent the time checking out Crystal and digging through what is available, and wrote it all down as I learned.Download a PDF, MOBI, or EPUB or read online for free.
I love new programming languages, and while I've been using Ruby for the past few years, I've coded in Java, PHP, Crystal, Elixir and a host of others. I also love writing, and good documentation, which is hard to find. Crystal doesn't have a lot of that yet, so I'm pitching in!
The contents of the three are exactly the same: I generate them both from the same source.
Really, I love alliteration: the only thing the 'for Rubyists' really means is that I assume you don't know about types, pointers, concurrency, or similar things. That's okay, you've never had to think about them before! I explain this stuff in extra depth. If you program in another dynamically typed language, you'll be just fine. If you program in another typed language, you'll be more than fine.