tools

• Gherkin is the language that Cucumber understands. It is a Business Readable, Domain Specific Language that lets you describe software’s behaviour without detailing how that behaviour is implemented.

Gherkin serves two purposes — documentation and automated tests
https://github.com/cucumber/cucumber/wiki/Gherkin

• Rspec is a story runner tool, Cucumber is a BDD feature flow explanation

and Capybara is the automation library where all the elements and
pre-defined objects are found. All together Capybara, Rspec and Cucumber
allows an user to automate the scripts and run them.
http://code.tutsplus.com/tutorials/ruby-for-newbies-testing-web-apps-with-capybara-and-cucumber--net-21446