OpenSees viz. Open System for Earthquake Engineering Simulations is an open source software framework for structural and geotechnical applications in both sequential and parallel environments. It has been developed in the research community as a means of sharing research ideas and developments via a common software platform. It has elements and materials for structural beam-column analysis and continuum analysis, geotechnical analysis and soil-structure interaction. It provides many options for solution algorithms, integration schemes, and equation solvers. A number of applications are provided for sequential and parallel usage.
The initial design of the framework is outlined Object-Oriented Finite Element Programming: Frameworks for Analysis, Algorithm and Parallel Computing. Some of the interfaces in the dissertation have been modified over time. Over time there has been many additions made to the framework, though the original design has remained basically the same. There have been many people who have contributed greatly to the framework over time. Their contributions are noted in the classes that they have developed. Due to its advanced capabilities of analysis and result interpretation it can be treated as reliable and user friendly package in the domain of Earthquake Engineering analysis