Selenium Testing Tool

• It is  automating web applications for testing purposes.
• Not a tool, but an API.
• Supports multiple browsers.
• Supports multiple languages,Operating systems.(PHP,Java,C#,Ruby)
• can integrate with other APIs as well(JUnit,NUnit,TestNG) 
• Open Source
•  Google developers are working on this API.
• Four components- Web driver,IDE,Grid,Remote Control.

Selenium Web Driver 

Browser based regression tests 

Selenium IDE

A Firefox add-on that will do simple record-and-playback of interactions with the browser.allows us to record, edit, and debug tests.

only work on Firefox.