SELENIUM is a free (open-source) automated testing framework used to validate web applications across different browsers and platforms. You can use multiple programming languages like Java, C#, Python, etc to create Selenium Test Scripts.
Selenium supports all the browsers available currently. Selenium web driver automation framework is crucial for web-based test automation. It is an extension to Java that provides property to platform independence. Selenium is the detector tool for both PC browser and mobile browser automation and is considered as a web standard supported by all browsers like Mozilla Firefox, Google Chrome, and many more.
As far as automation testing is concerned, Selenium Automation Testing is leading in the marketplace as of now.
Selenium has a wider scope and its future is as sharp as tools are emerging to make and support Linux, Windows, and OSX.