teamcapybara/capybara ? reverse-engineered prompt

Build me a Ruby library for acceptance testing web apps that feels like a real person is using the site. I want to be able to visit pages, click buttons and links, fill in forms, check for text, work with modals and windows, and wait for Ajax stuff without having to add a bunch of manual sleeps. It should work nicely with both Rails and plain Rack apps, and support switching between a fast headless style driver and a real browser without changing the test code. Please include easy setup for RSpec and Cucumber, plus a simple DSL that reads naturally in tests. Make sure the project is packaged like a proper gem, with solid specs and feature tests, and include the common drivers already wired up if possible. If you need to, look up current docs online to match modern Ruby and browser testing setup.