This paper describes a package of highly interactive simulation models for the concepts taught in Theory of Computing courses. Macintosh Hypercard stacks are used to demonstrate the three basic automata models: Finite-State Machines, Push-Down Machines, and Turing Machines. These simulations feature multiple named machines on the same stack, accessible via a customized menu or buttons on the screen. Because of the scripts hidden behind the visible screen, with just a click of a butto students can alter starting states, the set of input symbols, the number of states, the finality of states, or the action based on a given state/input combination. These simulations have been successfully used in conjunction with a course on the Theory of Computing at Union College since 1989. Students have responded enthusiastically to this concrete method of teaching abstract concepts.