ASCEND is a flexible modelling environment for solving hard engineering and science problems. It offers:
an object-oriented model description language for describing your system,
an interactive user interface that allows you to solve your model and explore the effect of changing the model parameters, and
a scripting environment that allows you to automate your more complex simulation problems.
ASCEND was originally written at Carnegie Mellon University in the 1980s and includes powerful and reliable solver routines that analyse the structure of your model and can solve thousands of simultaneous nonlinear equations in a few seconds on everyday computer hardware. It is under active development and is licensed under the GNU General Public License ensuring that it is free software and will remain free.