Increasingly, the sites designers and developers build aren't static pages any more. They are generated by applications like blogging systems, content management systems, or custom apps built with ASP, Rails, PHP and more.
These all present a particular challenge for developers - how can we style them when there aren't any static pages work with? Style Master solves this really difficult problem by allowing you to use online documents (and those running on local servers) as preview documents. You can then use all the features of the Design Pane, like X-Ray, to design your styles sheets. No other software lets you do this. It's features like these which make Style Master the only real choice for professional developers.
Editing a blog style sheet (click for full size image)