I do not use mac OS-X myself, but there are two very good SWI-Prolog editors that are cross-platform (thus also work on OS-X):
- PDT works with the Eclipse IDE. It has good syntax coloring, an in-IDE Prolog console, a dynamically generated visualization of the call graph, to name only a few of the many features it has. See http://sewiki.iai.uni-bonn.de/research/pdt/docs/v2.1/start I believe refactoring of Prolog code is not there yet, but the developers plan to add that cool feature in the future as well.
- PCE Emacs, an Emacs implementation by Jan Wielemaker that uses SWI-Prolog's graphical library XPCE. The UI elements look very Windows '95-ish, but don't be fooled by mere appearances here. PCE Emacs is completely tuned to SWI-Prolog and is probably the most versatile editor for SWI-Prolog out there. You can simply run it from within the SWI-Prolog console by typing
emacs.
Hope this helps!