Wikipedia
OpenModelica
OpenModelica is a free and open source environment based on the modelica modeling language for modeling, simulating, optimizing and analyzing complex dynamic systems. This software is actively developed by Open Source Modelica Consortium, a non-profit, non-governmental organization. Open Source Modelica Consortium is run as a project of SICS EAST Swedish ICT which is partially owned by Linköping University.
Even though OpenModelica is not as widely used as other commercial Modelica implementations, some of the industrial products use OpenModelica along with proprietary software in the fields of power plant optimization, automotive and water treatment.