Top 15 Most Installed free Drupal 8 theme: given below list of top most installed free Drupal 8 theme.
1- Bootstrap:
Download: https://www.drupal.org/project/bootstrap
2- Adminimal – Responsive Administration Theme:
Download: https://www.drupal.org/project/adminimal_theme
3- ZURB Foundation:
Download: https://www.drupal.org/project/zurb_foundation
4- Barrio:
Download: https://www.drupal.org/project/bootstrap_barrio
5- AdaptiveTheme:
Download: https://www.drupal.org/project/adaptivetheme
6- Drupal8 Zymphonies Theme:
Download: https://www.drupal.org/project/drupal8_zymphonies_theme
Live Demo https://demo.zymphonies.com/free-theme/d8/drupal8-zymphonies-theme/
7- Nexus Theme:
Download: https://www.drupal.org/project/nexus
8- MAYO:
Download: https://www.drupal.org/project/mayo
9- Drupal 8 Parallax Theme:
Download: https://www.drupal.org/project/drupal8_parallax_theme
Live Demo: https://demo.zymphonies.com/free-theme/d8/drupal8-parallax-theme/
10- Business:
Download: https://www.drupal.org/project/business
11- Bootstrap Business:
Download: https://www.drupal.org/project/bootstrap_business
12- Showcase Lite:
Download: https://www.drupal.org/project/showcase_lite
13- Zircon:
Download: https://www.drupal.org/project/zircon
14 – Material Admin:
Download: https://www.drupal.org/project/material_admin
15- Business Responsive Theme
Download: https://www.drupal.org/project/business_responsive_theme
Live Demo: https://demo.zymphonies.com/free-theme/d7/business-responsive-theme/