We sketch the fundamental properties and features of Snoopy, a tool to model and execute (animate, simulate) hierarchical graph-based system descriptions. The tool comes along with several pre-fabricated graph classes (in particular some kind of Petri nets and other related graphs), and facilitates a comfortable integration of further graph classes due to its generic design. To support an aspect-oriented model engineering, different graph classes may be used simultaneously. Our tool runs on Windows and Linux operating systems, and is available free of charge for non-commercial use. 1 Preliminaries Snoopy [Webd] is a generic and adaptive tool for modelling and animating/simulating of hierarchical graph-based formalisms. While concentrating our development as far on several kinds of Petri nets and related graph classes, the generic design of Snoopy facilitates also a comfortable extension by new graph classes. The simultaneous use of several graph classes is supported by the dynamic ada...