OpenSees, the Open System for Earthquake Engineering Simulation, is an object-oriented, open source software framework. It allows users to create both serial and parallel finite element computer applications for simulating the response of structural and geotechnical systems subjected to earthquakes and other hazards. OpenSees is primarily written in C++ and uses several Fortran and C numerical libraries for linear equation solving, and material and element routines. The framework WILL BE covered in the developers section.The goal of the OpenSees development is to improve the modeling and computational simulation in earthquake engineering through:new open-source code developmenteducationcommunity discussionA number of simple applications are provided to introduce new users and non-programmers to the OpenSees framework. All these applications are interpreters and they allow users to perform finite element analysis using a simple yet powerful scripting language. The analysis can look like plain text input files or they can be complex programs. It's up to the skills of the user. These applications are covered in the users section.