GreenHat makes certain variables available to templates (layouts, includes etc.) and they are used extensively. Those variable are as follows:

$catsThis is an array of all the categories used on the site.
$collectionsThis is an array of all the collections used by the site.
$layoutsThis is an array of all the layouts used by the site.
$menusThis is an array of all the menus used by the site.
$pageThis is the YAML front-matter data pertain to the individual page you are on. It will be a combination of the layout’s front-matter, overlaid and overwritten by the page’s own front matter.
$pagesThis is an array of all the pages in reverse chronological order.
$pagingThis is the paging control array used by the home page(s).
$postsThis is an array of all the posts in reverse chronological order.
$setsThis is an array of all the sets used by the site.
$siteThis is all the site data (basically everything in _config.yaml).
$tagsThis is an array of all the tags used on the site.

Example

If for example you wanted to print out the titles of all the posts, you’d do something like this in a smarty template:

{foreach $posts as $p}
    {$p.title}
{/foreach}