Selenium is an open source tool used for automating web application testing. It allows testing of applications across different browsers and operating systems. Selenium IDE is a simple record and playback tool that is installed as a Firefox add-on. It allows recording, editing and playing back tests without needing to learn a programming language. Selenium RC allows tests written in programming languages to be run on multiple browsers on remote machines. The latest version is Selenium WebDriver which supports test automation using various programming languages.