The CIAO modelling and fitting tool. Performs forward fitting of models to data in N-dimensions. Sherpa is "domain independent" ie. it does not require particular axes to be fit. Sherpa is also mission independent, with no particular tie to Chandra data - it has been used to analyze, e.g. HST spectra. Sherpa has a library of optimization methods and fit statistics in order to cope with the complicated parameter space inevitable in fitting N-dimensional data.

Sherpa also includes the "S-Lang" run time compiled language which can be used for scripting and data manipulation.

The GUIDE package within Sherpa links fit results (stored in a MDL file) to the ATOMDB, enabling the identification of spectral lines, and the use of their properties in further fitting.

The Sherpa threads page shows you how to use Sherpa. For more information, see the Sherpa web site.