Drupal is designed to be a strong core with configurable parts that work together. Drupal Commerce is designed from the ground up to take advantage of all Drupal 7 modules, but there are also a large number of commerce-specific modules.
The themes listed here lay the groundwork for your own custom Drupal theme and some of them even give you bit of unique styling for products, add to cart buttons, etc.
Distributions provide site features and functions for a specific type of site as a single download containing Drupal core, contributed modules, themes, and pre-defined configuration.
A sandbox project is a module or theme that contains experimental code that is not yet ready for general use. These are listed here to help the community find "starting points" for ideas that have not solidified into a distributed module.