Nightwatch.js is an automated testing framework designed for end-to-end testing of web applications and websites. Built on Node.js, it uses the W3C WebDriver API to interact with browsers and supports popular testing frameworks like Mocha and Cucumber. Nightwatch.js allows developers to write and run tests easily, facilitating continuous integration processes. It offers a user-friendly syntax and provides powerful features, such as parallel test execution, testing across multiple browsers, and live browser testing, helping ensure the reliability and performance of web projects.