Selenium is the most popularly used freeware and open source automation tool. The benefits of Selenium for Test Automation are immense. Importantly, it enables record and playback for testing web applications and can run multiple scripts across various browsers.
Some of the uses of Selenium are:
Faster report generation
Enable frequent regression testing
The infinite number of iterations can be done without deadlock
Can easily find errors that are missed in manual testing
Supports Agile methodology
Documentation becomes easier