The "best of Drupal" curated by Acquia
The intent of Lightning is to provide a lightweight framework for building working solutions in Drupal. Our components are managed as decoupled Lightning Features. If you're looking to build site with Lightning, just add Lightning Features to your project.
Fast & Feature Rich Drupal
A solid Drupal starterkit, Lightning provides reusable features that can be added to any Drupal project. One example of this is Acquia's DF, a robust buildout with its own custom content scenarios that showcase Drupal.
This particular project (the Lightning profile) showcases all Lightning Features working together. If you are interested in building a site of your own "on top of Lightning" you'll want to include Lightning Features as a part of your install profile. Read more about this concept in the docs.