Earlier quoted context omitted.
Racket isn't Scheme. It is its own dialect. That's why it's no longer called Scheme. At present, there are only a few Schemes that are practical: Chicken, Guile, Chez, and Gambit seem to be the big players, with Cyclone, Chibi, and Bigloo bringing up the rear.
Wow, pedantic much? It started out as a pure Scheme, then "took a practical turn" as the parent said. You can still make it act like a pure Scheme with a #lang directive. It's also kind of funny that a handful of major, practical implementations is considered a low amount. Number of Python implementations? Between one and three, depending on definition. Number of Javas? 2 or 3 again. Number of Clojure implementations…
At least three:
- Clojure on the JVM: https://github.com/clojure/clojure
- ClojureScript (JavaScript): https://github.com/clojure/clojurescript
- Clojure on the CLR: https://github.com/clojure/clojure-clr