Selenium Core = had the problem with the same-host policy, meaning that it enables to access the webpages within the same HOST. www.rustam.com, www.rustam.com/hello, it didn’t allow to access other websites like google.com, access to code elements is denied or blocked when using external script.
To avoid this complication, they developed a server component that enables you to test a web app with a test script that makes the browser believe that both are from the same source.
Selenium RC (Remote Control) - stand-alone server using an HTTP proxy, with Selenium Remote Server and Remote Client.
The time it took both the server and the client to receive and send HTTP requests led to the slower execution of test cases
Selenium Grid - enabling concurency running on different OS, with different browsers
Selenium Webdriver - consists of Selenium client libraries (Python, Java), browser drivers, and web browsers. The communication among the components is done through a JSON protocol.
