Whether you are just getting started with Drupal or you want to try something new, setting up your site with a new theme can make all the difference and while most of the best themes come from premium developers, you can try a few premium themes from drupal.org theme directory that are absolutely free to use.
There are plenty of great free themes available in the Drupal directory but its a mixed bag so i went through the theme directory and created a list of top 12 Free premium Drupal 8 themes.
Nexus theme is an elegant and flat responsive Drupal theme design. This theme could easily be used for a blog, small business, portfolio or a variety of other websites.
Zircon is a multipurpose theme that fearures a clean and soft-styled design with smoothly flowing structure. This theme is best suited for a business, company, or corporate to showcase their products or services on the site or an individual wishing to create a blog, or a personal site.
Bootstrap Business for Drupal by More than (just) Themes is a responsive Drupal theme, that helps you create a great-looking corporate/business site.
Drupal8 Zymphonies Theme is a responsive Drupal 8 theme with many features. It provides one, two and three column layout pages and multi-level responsive drupal menus.
Business theme is a very light weight theme with modern look and feel. This theme's clean layout and light weight code make it a great theme for small or medium-sized business to get up and running quickly.
Creative Responsive Theme is very light weight with modern look and feel.
The Business Group Zymphonies Theme is a Drupal 8 Responsive theme. This theme is fully customizable, Built with Bootstrap 3, It is suitable for any kind of Business Websites. This theme is completely free and contributed by Zymphonies team.
FontFolio is a Responsive showcase theme for designers, artists and craft persons. It presents full width/liquid grid layout for front page and categories pages, and 2 column layout for inner pages.
Paxton is a Drupal 8 multipurpose theme based on Twitter Bootstrap framework. It is a good choice for your Business, Corporate or Portfolio websites.
Clean blog is a carefully styled Bootstrap blog theme that is perfect for personal or company blogs. This theme features four HTML pages including a blog index, an about page, a sample post, and a contact page.
Business Responsive Theme features HTML5 and super clean markup, responsive hero banner, multi-level dropdown menus, 16+ regions and much more.