Everest is a base theme for Drupal.
Sub-theme can be easily generated by using the Drush command. $ drush everest-subtheme
$ drush everest-subtheme
Note: Currently it is in the development phase.
Black Drupal theme is powerful, clean, table-less, dark, responsive theme develop by Shivcharan Patil (Shiv) from itappliocation.net and Shiv.work.
Below are free themes built using Nucleus. This list is incomplete thus any contribution is greatly appreciated.