[cguess]

Ruby's type system is completely optional using separate definition files (except Sorbet, which isn't part of the core language), while Crystal's is built in and required.

[TranquilMarmot]

It also seems like Crystal is compiled, yeah? Would it be safe to say "Crystal is like Ruby but compiled and faster"?

[antifa]

You can also think of it as "what if golang had a real type system and ruby style syntax".

[dragonwriter]

Crystal is like Ruby but not dynamic, with macros, without reflection, with arbitrary API changes to the core types that are shared, with value/reference type dichotomy, compiled, and faster.

Or, with apologies to the late Douglas Addams, Crystal is almost, but not quite, entirely unlike Ruby.

[antifa]

Crystal has compile-time macros/reflection, instead of runtime.