Selenium - a set of tools for automated testing, consists of the following components:
Selenium IDE (Integrated Development Environment) is a Firefox plugin that allows testers to record their actions by following the workflow they need to test.
Selenium RC (Remote Control) was the flagship testing system, which allowed more than simple browser actions and linear execution. It used the full power of programming languages ​​such as Java, C #, PHP, Python, Ruby, and PERL to create more complex tests.
Selenium WebDriver - is the successor to Selenium RC, which sends commands directly to the web browser and retrieves the results.
Selenium Grid is a tool used for parallel testing on different computers and different browsers at the same time, which minimizes runtime.