Articles
Perl.com: Making Perl Reusable with Modules – step-by-step guide to building a Perl module
MacTech.com – Test-Driven Development Using AppleScript – includes an overview of the AsUnit test framework and an example of using it to develop a simple game.
Tutorials
Developing OPML Editor Tools – A seven-part series on creating Tools for the OPML Editor, an outliner and web application development environment based on Frontier (created by Dave Winer).