A "free browser that allows you to have the rendering and javascript engines of IE8 beta 1, IE7, IE6, and IE5.5 on Vista and XP, as well as the installed IE in the same process."

Invaluable for troubleshooting web development in IE. Wish I'd known about this before today!

"The MacPorts Project is an open-source community initiative to design an easy-to-use system for compiling, installing, and upgrading either command-line, X11 or Aqua based open-source software on the Mac OS X operating system."

Free Mac software for taking webpage screenshots. Can capture the entire length of a page (beyond the "fold").

"A tool for visual layout development of YAML based CSS layouts." YAML stands for Yet Another Multicolumn Layout.

"Striped background generator."

"JavaScript Regex Tester." Put in your test data and your regular expression and see if it works.

"HandBrake is an open-source, GPL-licensed, multiplatform, multithreaded DVD to MPEG-4 converter, available for MacOS X, Linux and Windows."

A list of online collaboration tools.

Some very useful utilities. Service Scrubber helps you manage OS X services, Witch turns command+tab into something that can access the windows of individual applications, not just the applications themselves.