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