Themes allow you to change the look and feel of your Drupal site. You can use themes contributed by others or create your own to share with the community. Contributed themes are not part of any official release and may not have optimized code/functionality for your purposes.
You can also create a sub-theme of an existing theme. A sub-theme inherits a parent theme's resources. Read more about Sub-theme structure and inheritance.
You can also view a full index of themes listing only their titles.
The goal of this base theme is to rewrite most of the core themes functions of Drupal and use proper render arrays and templates instead. This will allow users to customize at will most of the elements in a custom sub-theme using preprocess/process functions or by providing a custom template.