HYPENS is an open source tool to simulate timed discrete, continuous and hybrid Petri nets. It has been developed in Matlab to allow designer and user to take advantage of several functions and structures already defined in Matlab, such as optimization routines, stochastic functions, matrices and arrays, etc. The tool can also be easily interfaced with other Matlab programs and be used for analysis and optimization via simulation. The large set of plot functions available in Matlab allow one to represent the results of the simulation in a clear and intuitive way.