I am looking for a version of Scheme or even LISP that I can use to recover some lost Lisp development skills. Some web capabilities would be nice but not essential.
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Depending how you define "Lisp", Clojure may fit the bill. It runs on OS X fine (it runs anywhere the JVM runs). It has web capabilities and it's free.
It also has the benefit of being new and fresh and fun to use. Might be ideal for hobby programming. It's easy to write web apps or GUI apps (using Java's Swing or even Qt).