Selenium is a tools suite to automate web browsers, and web application testing
Selenium is a portable software testing framework for web browser automation. The Selenium IDE provides a record/playback tool for authoring tests without learning a test scripting language. Selenium provides a test domain specific language (DSL) to write tests in a number of popular programming languages, including Java, C#, Ruby, Groovy, Python, PHP, and Perl. Test playback is possible in most modern web browsers. Selenium deploys on Windows, Linux, and Macintosh platforms.
Selenium 2 WebDriver, the successor to Selenium 1, is the second installment of Selenium, and ties directly into the browser API that is provided by the browser manufacturer.
Selenium was originally developed by Jason Huggins, who was later joined by other programmers and testers at ThoughtWorks. It is open source software, released under the Apache 2.0 license and can be downloaded and used without charge.
Selenium IDE is a complete integrated development environment (IDE) for Selenium tests. It is implemented as a firefox extension, and allows recording, editing, and debugging tests. It was previously known as Selenium Recorder. Selenium IDE was originally created by Shinya Kasatani and donated to the Selenium project in 2006.
Selenium Builder is a record and playback integrated development environment (IDE) for Selenium tests. It is implemented as a firefox plugin, and allows recording, editing, and debugging tests. It was initially created by SauceLabs and the source code base was given to the Selenium project with the plan to eventually replace 'Selenium IDE'.