atck was developed in a production environment for purposes of quickly building css and xhtml valid Drupal themes from scratch without having to un-theme an existing Drupal theme to do it.
1. WYSIWYG grid builder
A browser-based grid builder which produces starter code for a page.tpl.php file. The grid builder itself was originially built by Christos Constandinou and it uses a modified version of Yahoo Grids which is more flexible and easier to customize. With Christos' permission it, and the supporting css, has been customized so that it works for Drupal themes and so that it is css3 valid. Access the builder online (FF only!), or download it and run it locally. [builder version controlled at Google projects because cannot be on Drupal.org because of MIT license]
2. style.css [separate download - version controlled at Google projects because of BSD license - ]
style.css contains only the css needed to support what the grid-builder outputs, as well as some general 'resets'. The only modifications one should need to make here would be if they want to make their layout a fixed width and/or a different width (default widths are in %).
3. page-layout.css and template.php
These files are where the visual styling of the site happens. The source of these files is from a combination of code from the Hunchbaque theme and some changes/additions which I added in order to provide baseline settings I prefer and/or provide more granular settings. The beauty of these files is the simplicty of them - they include as little markup/styling as possible to avoid complexity, while at the same time putting many helpful tools/comments at your finger tips so that you can accomplish what you want.
A sample page.tpl.file is included as a reference for finishing your own page.tpl.php file using code output from the grid builder. Note particularly the variable names for the blocks, regions, menus, etc. (at this point the builder does not include those items)
5. fix-ie-6.css and fix-ie-7.css
These files are included for purposes of providing IE-only css to each of the respective versions. By using conditional comments like this we keep the main css files hack-free and atck css3 valid.
Please note: ATCK for Drupal 5 is very sturdy, but all the new features are going into ATCK 6.x, and the Drupal 5 version is no longer really under active development