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.
Webinject - WebInject is a free tool for automated testing of web applications and web services.
Screenster - 10x faster UI testing without a line of code.
httest - The httest provides a large variety of HTTP-related functionality, useful for implementing all...
UI.Vision - Modern open-source task and test automation tool and Selenium IDE.
SlimerJS - A scriptable web browser for web testing, web scraping, network monitoring...