This website was created to demonstrate the features of the Style Guide module. Style Guide is a unique module that helps designers create comps that are easier for themers to theme, while helping themers take note of the parts of a Drupal site that are often neglected.
Check out the Style Guide documentation for more information.
From d.o:
Provides a visual testing page for Drupal themes. Quickly compare the display of common elements across your themes, and verify that your new theme addresses all common style elements.
The Style Guide module creates a preview page for displaying common theme elements in all active themes for your Drupal site. The module comes with previews for common HTML elements, such as tables, forms, links and lists.