Based off of Rename which worked with Rails 3 apps.
Rename is a gem for Rails 4+ applications which renames the app. To run, simply install the gem by adding this line to your gemfile:
gem 'rails-rename', '~> 1.0.0'
Then, run bundle install to install the gem.
If you want to install it manually, simply run:
gem install rails-rename
rails g rename NewAppName
where NewAppName is the new name for your application in camelcase.