What is "opensees"

OpenSees, the Open System for Earthquake Engineering Simulation, is an object-oriented, software framework created at the NSF-sponsored Pacific Earthquake Engineering (PEER) Center. It allows users to create finite element applications for simulating the response of structural and geotechnical systems subjected to earthquakes. This framework was developed by Frank McKenna and Gregory L. Fenves with significant contributions from Michael H. Scott, Terje Haukaas, Armen Der Kiureghian, Remo M. de Souza, Filip C. Filippou, Silvia Mazzoni, and Boris Jeremic. OpenSees is primarily written in C++ and uses several Fortran numerical libraries for linear equation solving.