Other than being a statically typed language: Crystal AOT compiles down to native code (so, good FFI) and has a much better portability story (you can port it to ~any LLVM target).

All that Graal stuff, while a true open source project, has some "Oracle weirdness" around it (IIRC, only Linux (and probably only amd64) is supported in the "community edition") and requires JDK 9/10 (not available on FreeBSD yet..)

That's about speed (though I think Truffle/Graal make an app consume more memory). Crystal is type-safe, and no optimizing VM can do that for Ruby.

Not that type-safety is a killer feature, but that's just one difference.

Some people (myself included) actually want the type safety and method overloading etc. Also you can only make a dynamic language so fast before there are inherent trade-offs.