The solver has been applied to models as large as 120,000 elementary reactions, and can be readily via a spreadsheet mechanism which eliminates the need for users to code in reactions by hand. The code is available for free download, and appears to function on most UNIX systems.
Documentation is provided with the distribution file.
These codes have been vectorized for Cray supercomputers, and parallel versions are available for SGI architectures. Input entails simple input of chemical species and chemical reactions lists. Only the calling routine from the model needs to be altered. No online documentation is provided, but a detailed manual comes with the distribution and can be viewed graphically or printed out. The main package is not freeware, but they do have a smaller version entitled EQS4WIN Lite which is available for free dowwnload.