When you design web sites in the browser you're left alone in the dark without any of your familiar design tools. By nature there's no application you can load up and start building your design. Well, this isn't that. However I think it's the next best thing.
The Coding Designer's Survival Kit is two related projects. First is the project on Github, which is not Drupal, but a generalized set of tools for doing this work in any CMS (or none). Second is the theme based on that project, which will have a full release here on drupal.org shortly.