newLisp(tm) for GNU/Linux, BSDs, MacOS X, Solaris, Win32
From their web site: "newLisp is a general purpose scripting language for developing web applications and programs in general and in the domain of artificial intelligence (AI) and statistics?." From the CLiki home page: "Links to and resources for free software implemented in Common Lisp and available on Unix-like systems".
This is *NOT* Common Lisp, but if you're migrating from Python, Ruby, Perl, etc, this may be just what you're looking for. Likewise, if you need/want one consistent Lisp-like system to run on various platforms, consider using this for a while... then come back to Common Lisp... or not.
Be sure to see this page on their site: Differences to Other LISPs.
CLiki pages can be edited by anyone at any time. Imagine a fearsomely comprehensive disclaimer of liability. Now fear, comprehensively