The book explains in detail how the Eclipse technologies: Eclipse Modeling Framework EMF, Graphical Editing Framework GEF, Graphical Modeling Framework GMF, and Java Emitter Templates JET can be used to develop graphical design tool. The development process is explained using the X-Machine toolkit case study. X-Machine is one of the effective formal methods that can be applied to the system specification phase to represent the model of the system formally and precisely using a combination of easily understood diagrams and very precise words. Then the X-Machine model is used to generate an implementation of the system and to develop a complete functional testing method for the system. The developed X-Machine toolkit within Eclipse platform has a professional look and feel. The implemented toolkit allows the user to construct X-Machine models diagrammatically, store the constructed models specifications in XML format, validate the data of the constructed models to make sure that it confirms to the constraints placed on that data, generate Java code from the constructed models, animate the X-Machine State-Transition diagram, and generate test cases from the constructed model.