Cypress

Cypress completely disrupted the dominance of Selenium in the web testing space by offering a radically different architecture. Selenium is "out-of-process"—it runs outside the browser and sends remote commands to it via the network, which causes massive latency and the infamous "flakiness" where tests fail just because a page loaded a millisecond too slowly. Cypress runs "in-process." The testing code runs in the exact same run-loop as the web application itself inside the browser. This means Cypress has native access to the entire DOM (Document Object Model), the network layer, and local storage. Tests in Cypress run incredibly fast and are mathematically immune to the "network wait" flakiness that plagues Selenium. It is heavily beloved by modern frontend developers (specifically those building React, Vue, or Angular applications) because it provides "Time Travel." As a test runs, Cypress takes snapshots of the DOM at every single step. If a test fails, the developer can literally hover over the exact line of code that failed and see a perfect visual snapshot of exactly what the browser looked like at that exact millisecond.