Selenium was initially a JavaScript library developed by Jason Huggins in 2004 .It was able to interact with browser and automate the tasks on multiple browsers.This forms the Selenium core which is beneath Selenium RC and Selenium IDE. There were many limitations due to the restrictions of JavaScript in browsers.Later in 2004 Simon Stewart developed a tool that interacts directly with the browser.This project was called Web Driver.In 2008 they merged these two tools to make the current Selenium 2.0.
Selenium is collection of following tools.
- Selenium 2 (Web Driver).
- Selenium 1(Selenium RC).
- Selenium IDE.
- Selenium Grid.
Each tool serves different purpose.Selenium Grid allows you to run your tests in parallel.Selenium IDE makes record and play tests.Its recommended to learn Selenium 2 as it is going to be supported in future.