Purpose: to gather into one place references and material regarding tools a developer might use to create the framework of an application with a GUI.
Sometimes, people recommend A poor mans GUI when a question about GUI Building Tools come up. Its form-based model applies to many (most?) GUI applications.
Sometimes people confuse a GUI builder with an integrated development environment (aka IDE). A GUI builder typically is just about building the GUI, and seldom has debugging facilities, code management capabilities, etc. Komodo is an example of an IDE with GUI builder.