The functionality provided by GUIKit has been superseded by the interface construction and controls functions native to the built-in Wolfram Language.
GUIKit Example: GraphEditor
This example demonstrates the benefit of supplementing Wolfram Language functionality with GUIKit user interface elements leveraging existing third-party graph model and editing libraries. GraphEdit widgets take advantage of the Graph expression supported by Combinatorica` and also SparseArrayArrayRules.
The user interface of the graph editing canvas allows you to do the following.
Create a new node (Ctrl+click or Right (alternate) click).
Create a new edge (Ctrl+click or Right (alternate) click inside a node).
Move selection (Drag selected nodes and edges).
Change selection (Drag, click, or Shift+click).
Delete currently selected nodes and edges (Del or Backspace key).
Here is another version run in a modeless session where you can interact with and change the displayed graph.