That is a plugin to work with user stories in factbox.
Add this line to your factbox's Gemfile:
gem "kanban", git: "https://github.com/factbox/kanban"
If you want use locally:
gem 'kanban', path: 'path_to_dir/kanban'
So, in factbox root you can:
$ bundle install
$ rails g install kanban
This will create some migrations, so you should run:
$ rails db:migrate