The JBuilder UI

The JBuilder integrated development environment (IDE) consists of a window that contains several panes and panels for performing most development functions: editing, visual designing, navigating, browsing, compiling, and debugging. This window is called the AppBrowser.
Note: To expand this pane full width, choose View|Toggle Curtain on the menu (Alt+Ctrl+Z in CUA).

For more information, see:
Building Applications with JBuilder:  The JBuilder environment