Updated March 10, 2008: Clarified location of Extensibility documentation.

Flex Builder is a collection of Eclipse plug-ins that provide the tools you need to create Flex and ActionScript 3.0 applications. The Eclipse plug-in framework allows plug-ins to expose extension points, which can be used to extend the features and capabilities of the tool. For more information, see Adobe Flex Builder 3 Extensibility in the Flex Builder Help system.