OpenSees is a software framework for developing applications to simulate the performance of structural and geotechnical systems subjected to earthquakes. A number of OpenSees applications are released on this website. Here is a short video. The goal of the OpenSees development is to improve the modeling and computational simulation in earthquake engineering through open-source development. OpenSees is under continual development, so users and developers should expect changes and updates on a regular basis. In this sense, all users are developers so it is important to register. More information on Open Source is available. The development of OpenSees is sponsored by the Pacific Earthquake Engineering Research Center