twitter_bootstrap_sass was the first bootstrap provided by the community. It is deprecated and is no longer used.
bootstrap-sass-rails was the official bootstrap. This was provided by the community and approved by Twitter until it was deprecated in 2014 and replaced with a lower bootstrap sass
bootstrap-sass is the official bootstrap provided by Twitter for rails users. This is the currently recommended stone for adding bootstrap resources to your rails application.
Note (upgrade from Rails 5.1.2)
The currently recommended way to incorporate external assets is Yarn . Yarn is the interface package manager that ships with Rails 5.1.2. If you want to do this with Rails, just run yarn add bootstrap in your project directory, and Yarn will handle the bootstrap for you. You can then import the .css and .js boot files into the application manifest.
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