Gaffr.net is a modelling and prototyping tool from CapableObjects.com , contains a UML-class modeller, contains a UML-state machine modeller, lets you execute your model including the state machines, uses the standard OCL as constraint and query language, can reverse engineer existing databases, contains a prototyper so that you can verify your thoughts, brings you ModelDrivenArchitecture MDA, is designed for DomainDrivenDesign