In the past I have used Kawa and SISC Schemes a lot: good projects. However, Clojure has the momentum, community, etc.<p>I wrote a Scheme book for Springer-Verlag back in ancient history and I still use Gambit-C a reasonable amount and Racket is pretty cool also. So, I am not biased against Scheme, I am just saying that Clojure might be a better place to start if you want to experiment with Lisp languages on the JVM.