The Graphical Editing Framework (GEF) allows developers to create a rich graphical editor from an existing application model. GEF consists of 2 plug-ins. The org.eclipse.draw2d plug-in provides a layout and rendering toolkit for displaying graphics. The developer can then take advantage of the many common operations provided in GEF and/or extend them for the specific domain. GEF employs an MVC (model-view-controller) architecture which enables simple changes to be applied to the model from the view.
GEF is completely application neutral and provides the groundwork to build almost any application, including but not limited to: activity diagrams, GUI builders, class diagram editors, state machines, and even WYSIWYG text editors.
Reference:
http://www.eclipse.org/gef/overview.html
