What you can do with Flex Builder ?

Create Flex projects with or without using the Flex server. For more information, see Creating Flex projects.
Create ActionScript projects that use the Flash API. For more information, see About ActionScript projects.
Write and edit your application source code using editors that provide features such as code refactoring, code hinting, streamlined code navigation, and automatic syntax error checking. For more information, see About code editing in Flex Builder.
Use the MXML editor in Design mode to simplify using view states and transitions, to design using absolute layout options, to drag components onto the design canvas and then reposition and resize them as needed, and so on. For more information, see Building a Flex User Interface.
Create ActionScript functions within your MXML code or as separate files of ActionScript functions, classes, and interfaces.
Create custom components and then easily access them using the Components view. For more information, see Creating Custom MXML Components.
Manage your application projects by using the many features provided by the underlying Eclipse IDE. For example, you can add and delete projects and resources, link to resources outside your project, and so on. For more information, see Managing projects and Creating folders and files in a project.
Build your applications using predefined builders or create custom builders using Apache Ant. For more information, see Building Projects.
Run your applications in a web browser or the stand-alone Flash Player. Create custom launch configurations to control how your applications run. For more information, see Running your applications and Managing launch configurations.
Test and debug your applications using the integrated debugging tools in Flex Builder. For more information, see Running and Debugging Applications.
Publish your application source code so it can be viewed by users and other developers. For more information, see Publishing source code.
Create library projects that generate shared component library (SWC) and run-time shared library (RSL) files for code reuse and distribution. For more information, see About library projects.
Customize the IDE. For example, you can arrange the interface to include your favorite tools in the specific layout. For more information, see Navigating and Customizing the Flex Builder Workbench.