Lightning is end-of-life.
Acquia ended support for the Lightning distribution on November 2, 2021, simultaneously with Drupal 8. Lightning 3, 4, and 5 no longer receive any security updates or bug fixes. It is possible to safely uninstall Lightning from your site; please see the official announcement, FAQ for site owners, and developer instructions for more information.
The intent of Lightning is to enable developers to create great authoring experiences and empower editorial teams. We do this by providing a lightweight framework, documentation and best practice examples for building working solutions in Drupal.
We have taken advantage of new D8 functionality and tightly coupled functional areas we consider to make up the new standard for enterprise authoring in Drupal including Layout, Workflow, Media, and API. We have also embedded dozens of automated tests allowing developers to implement continual integrations pipelines that monitor major functionality, essentially providing a safe environment to innovate with their own custom code additions to Lightning.