Selenium IDE is an integrated development environment for Selenium scripts. It is implemented as a Chrome and Firefox extension, and allows you to record, edit, and debug tests.
Selenium IDE is not only a recording tool: it is a complete IDE. You can choose to use its recording capability, or you may edit your scripts by hand. With autocomplete support and the ability to move commands around quickly, Selenium IDE is the ideal environment for creating Selenium tests no matter what style of tests you prefer.
Selenium IDE has plugin support. For details, see the Getting Started with Plugins project wiki page.