Selenium is an open source framework for testing web applications. Use for questions about testing with Selenium 1, Selenium IDE, and to a lesser extent, Selenium WebDriver.
Selenium was developed as an extension for firefox to allow testing of web applications. It is open source and may be downloaded from the project's website.
Selenium offers record and playback through a Firefox Integrated Development Environment (IDE). For automated test cases a variety of languages is supported through multiple Application Programming Interfaces (API's). Browser specific drivers allow for more simple command based browser control. Tests can be run parallel or remotely.
In addition, many popular tools offer Selenium integration.