As gammafactor notes, Racket is not Common Lisp. Nor does it have any other implementations, free or proprietary. That's one of the great advantages of Common Lisp: a single standard, implemented multiple times by multiple people, running on many platforms.
Racket is definitely neat. I don't know for certain, but I hope it learns from some of the same lessons that CL learned from. Still, why not use the standardised, industrial-strength Lisp?
> But the title of the post wasn't a Common Lisp ... it was a Lisp interpreter which technically Racket is a Lisp.
Common Lisp is Lisp: it's a standard which specifies the minimum required functionality of a Lisp implementation. Anything which doesn't meet that standard isn't Lisp.
Scheme, Racket, Hylang, Clojure may each be a Lisp, but none is Lisp (unless one of them has bothered to implement the Common Lisp standard).
Racket is definitely neat. I don't know for certain, but I hope it learns from some of the same lessons that CL learned from. Still, why not use the standardised, industrial-strength Lisp?