MCLIDE
MCLIDE is a free open source Macintosh IDE for Lisp implementations on any platform. It is a double-clickable, stand-alone GUI based lisp development environment that connects to a Lisp either locally or through the network using SWANK. The MCLIDE Lisp IDE runs on MacOSX 10.4 and up (Intel or PPC). It can be used with many of the same Lisp implementations as SLIME/SWANK.

Homepage: http://mclide.com/