Development 

Adobe AIR 2.0.0.10760 Free Public beta of the next version of AIR.
http://www.adobe.com/products/air/
REQUIREMENTS Mac OS X 10.5 or later.
Adobe AIR is a cross-operating system runtime that allows web application developers to use their existing web development skills (HTML, Javascript, Adobe Flash, Adobe Flex, Ajax) to build and deploy rich Internet applications on the desktop. Adobe AIR enables developers to create applications that combine the benefits of web applications - network and user connectivity, rich media content, ease of development, and broad reach - with the strengths of desktop applications - application interactions, local resource access, personal settings, powerful functionality, and rich interactive experiences. Adobe AIR enables familiar application interaction models, including drag-and-drop support, rich clipboard access, and desktop and system shortcuts. Adobe AIR applications run as regular applications, and do not have to run within another application or shell (as web applications do by running within the browser).

Armadillo 1.0 Free Create startup items.
http://www.sveinbjorn.org/armadillo
REQUIREMENTS Mac OS X 10.3 or later.
Armadillo is a Mac OS X Cocoa application for creating Mac OS X startup items. Armadillo makes it very easy to create correctly formatted startup items that are fit for the /Library/StartupItems folder and subsequent execution at system booting. 

CocoaDialog 2.1.1 Free Create GUI frontends for shell, Perl scripts.
http://cocoadialog.sourceforge.net/
REQUIREMENTS Mac OS X 10.4 or later.
Create GUI frontends for shell, Perl scripts. CocoaDialog is an OS X application that allows the use of common GUI controls such as file selectors, text input, progress bars, yes/no confirmations and more with a command-line application. It requires no knowledge of Cocoa, and is ideal for creating frontends to shell and Perl scripts (or Ruby, or Python, or... etc).

Go4Launch 0.2 Free Universal Easily add startup tasks to Mac OS X using launchd services.
http://13cubed.com/
REQUIREMENTS Mac OS X 10.5 or later.
Go4Launch... Easily add startup tasks to Mac OS X using launchd services! Go4Launch does all the behind-the-scenes work and creates a "template" shell script that you can modify with a single click. Add your own commands to the shell script, save, and you're done!

HexEdit 2.2 Free Hexadecimal file editor for data and resource forks.
http://hexedit.sourceforge.net/
REQUIREMENTS Mac OS X 10.4 or later.
HexEdit is a hexadecimal file editor that handles both data and resource forks. It is the most widely used editor of its kind on the platform, and can handle file sizes of up to four gigabytes with ease, yet has memory requirements of less than a megabyte (with color turned off). It can compare whole files for similarities or differences and will soon be able to do so for any subset within the files. A great tool that allows you to edit and analyze the contents for either the data or resource fork of any type of file.

Lingon 2.1.1 Free Universal GUI for creating/controlling launchd config files.
http://sourceforge.net/projects/lingon/
REQUIREMENTS Mac OS X 10.5 or later.
Lingon is a graphical user interface for creating an editing launchd configuration files for Mac OS X Leopard 10.5. You can use launchd on a Mac to launch scripts and applications whenever something special happens or at a specific time or periodically. You get all launchd configuration files in a list to the left so you can easily see all and choose which one to edit.

Python 3.1.2  Free Object-oriented programming language.
REQUIREMENTS Mac OS X 10.3.9 or later.
Python is an interpreted, interactive, object-oriented programming language. It is often compared to Tcl, Perl, Scheme or Java. Python combines remarkable power with very clear syntax. It has modules, classes, exceptions, very high level dynamic data types, and dynamic typing. There are interfaces to many system calls and libraries, as well as to various windowing systems (X11, Motif, Tk, Mac, MFC). New built-in modules are easily written in C or C++. It is also usable as an extension language for applications that need a programmable interface.

SymbolicLinker 2.0v2 Free Universal Contextual menu creates symbolic links in Finder.
http://seiryu.home.comcast.net/~seiryu/symboliclinker.html
REQUIREMENTS Mac OS X 10.1 or later.
SymbolicLinker is a tiny contextual menu plugin (for Puma through Leopard users) and software service (for Snow Leopard & later users) that, once installed, allows any user to create symbolic links to files inside the Finder. SymbolicLinker does this by adding a contextual menu item to the Finder that generates symbolic links to the selected files. The goal of this product is to decrease users' trips to the Terminal in order to use the "ln -s" command. 

Tex-Edit Plus X 4.9.8 Shareware $15 Styled text and development editor.
http://www.tex-edit.com/
REQUIREMENTS Mac OS X 10.1 or later.
Tex-Edit Plus is a styled text editor that nicely accommodates users who require a little more than SimpleText can offer, without having to use a full-fledged word processor. It's fast, efficient, and has a clean, uncluttered interface. Users will also find it handy for cleaning up text received over the Internet.

TextWrangler 3.1 Free Universal Compose, modify and transform text files.
http://www.barebones.com/products/textwrangler/
REQUIREMENTS Mac OS X 10.4 or later. 10.6 tested
TextWrangler is a free, general purpose text editor that is very handy tool for developers. We recently made it free for people (in exchange for beer).