Selenium - Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that.
DalekJS - DalekJS is an open source UI testing tool.
Webinject - WebInject is a free tool for automated testing of web applications and web services.
Pincers - Web Automation API that runs on top of WebDriver
UI.Vision - Modern open-source task and test automation tool and Selenium IDE.
Cypress.io - Slow, difficult and unreliable testing for anything that runs in a browser. Install Cypress in seconds and take the pain out of front-end testing.