When turning on GitHub Pages for a repository, it will turn the contents of the repository into a very minimal website. I love the simplicity of having only a README.md and some auxiliary files turned into a minimal website with zero configuration needed.
To reproduce the rendered website locally, put the following content into a gemfile:
source "https://rubygems.org"
gem "github-pages", group: :jekyll_plugins
and run:
bundle install
bundle exec jekyll serve