Selenium provides support for the automation of web browsers. It provides extensions to emulate user interaction with browsers, a distribution server for scaling browser allocation, and the infrastructure for implementations of the W3C WebDriver specification.

Selenium automates browsers. That's it!

Atlassian WebDriver Core

OperaDriver is a vendor-supported WebDriver implementation developed by Opera Software and volunteers that implements WebDriver's wire protocol.

A suite of tools to help with Selenium test harness, assertions etc.

A Fluent API on top of Selenium's WebDriver API

Yandex QATools WebDriver Matchers

Minium Rhino Integration

This is selenese script interpreter implemented by Java. It supports test-case and test-suite which are Selenium IDE's native format.

The SenBot runner which will actually run all your acceptance tests and report the outcome

Minium Console