Selenium is a portable software-testing framework for web applications.
It provides a test domain-specific language (Selenese) to write tests in a number of popular programming languages, including:
Selenium deploys on Windows, Linux, and MacOS platforms.
It is open-source software, released under the Apache 2.0 license 
Seems to dominate the area for web UI automation
Web ‘drivers’ let’s you programmatically control different types of web browsers
- Internet Explorer or Edge
- HtmlUnit (headless browser)
Selenese let’s you interact with a web page’s elements
- Mouse movement, hovering, dragging