I've seen Crystal a few times in the past, though I haven't used it for a project so far. Looking at their website and issue tracker it looks like it would be r

I've seen Crystal a few times in the past, though I haven't used it for a project so far. Looking at their website and issue tracker it looks like it would be rather difficult to be able to hotload code if Crystal was used compared to MRuby (based upon the notes that a Crystal REPL isn't a primary feature as a compiled language). Additionally I can't find too many details (though I'm sure they're there) about the runtime requirements imposed by Crystal applications. One of the nice things about the MRuby implementation is that it makes it easier to combine all parts of your program (C extensions and ruby compiled to VM instructions) into a single binary with minimal external dependencies.