Excellent implementation of Common Lisp with a long history...

Clozure CL has its roots in MCL, the excellent Macintosh Common Lisp environment developed by Coral Lisp, and at one time actually owned by Apple. CCL is a new, high performance implementation for the Intel architecture. It also runs on Windows, but is a true OS X implementation.

Without question, it is the best Lisp on OS X.

HaraldS about Clozure CL