The philosophy of the Ptolemy Project is appealing, as it does not express heterogeneous models in terms of one general model of computation. Instead of that it uses an abstract semantics which every actor has to fulfill, and a director block in each actor implements the concrete rules of execution. This allows a rigorous coupling in hybrid models. Furthermore Ptolemy II is an open source software and freely available. Therefore it is possible to study the internals of the simulator and to do research on hybrid systems without expensive software. Still missing are advanced ODE or DAE solvers (2011).