AquaMacs is an Emacs build for OS X (unfortunately only from 10.3 onwards) that aligns more closely with the Mac OS X Human Interface Guidelines. Those who appreciate the high configurability of Emacs but not the rather sick interface and key binding for Mac users might want to check this out.
Archive 24. April 2005
The .emacs File by Bill Clementson. Shows very nicely why one should actually consider using Emacs. Particularly interesting for Common Lisp users is his customizing for Slime for integrating various Common Lisps.
Those who only occasionally work with PostgreSQL, so to speak, want to use it as a desktop database: PostgreSQLX is a compilation of the PostgreSQL server that can be easily started and stopped as a Mac application. Ideal for developers. Then also the PGAccess interface and you can do without something like Microsoft Access. Of course, all of this only from 10.3 (it's about time 10.4 comes out and I'm up to date at home again).
SPE-OSX comes from the same stable as AquaMacs and is a compilation of Stanis Python Editor - a very comprehensive IDE for Python. Also only available from 10.3.
sproutliner is a fun web application with which you can edit an outline over the web. Naturally heavily based on Ajax.