Xyle Scope

Just stumbled upon a great little Mac app for web developers called Xyle Scope. It's a web browser (that uses the Safari engine) that allows you to interactively view all the style sheet and XHTML information of the page or any element you click on in the page. You can interactively experiment with the CSS (and save the changes if the files are local), see at a glance what rules in which files are being applied to elements (including the cascading precedence), see padding and margins, browse the hierarchical structure of the XHTML, and even browse the DTD. Well worth checking out if you use a Mac to do your web development.