Xcos - Xcos is a graphical editor to design hybrid dynamical systems models.
EMSO simulator - EMSO simulator is an equation-oriented process simulator with a graphical interface for modeling...
Altair Activate - Altair Activate is an open & flexible tool for rapidly modeling and simulating products as multi-disciplinary systems in the form of 1D models (expressed as signal-based or physical block diagrams), optionally coupled to 3D models.
OpenModelica - OpenModelica – A Free Modelica Environment!
Minsky - System dynamics program with additional features for economics
Scicos - a graphical dynamical system modeler and simulator