- Fugu - Secure FTP. SCP etc. Hasn't really been updated in a while but it works pretty well. Allows you to edit remote files with your favorite local text editor.
- RegExhibit - Interactively test regular expressions
- Locomotive - Ruby on Rails in a box. A single standalone application that includes Ruby, MySQL, a web server, and an application to manage them all.
- MySQL 5.0
- Aquamacs Emacs - Holy union of emacs and Aqua. Normal emacs key bindings work (e.g. C-e end of line). Normal Aqua keybindings work (e.g. Cmd-a select all). Includes various elisp functions to bring emacs closer to the 21st century. All in a nice OS X native application with lots of polish.
- TextMate - Best text editor ever. (Sorry emacs).
- Transmit - Best FTP/SFTP/SCP client ever. Allows me to edit remote filew seemlessly with TextMate. These days I'm often connected to the internet intermittently or with high latency. Editing files in this idiom (which seems to be almost unique to the Mac) is the best way around that.