ISIS
ISIS, the Interactive Spectral Interpretation System, is designed to support the analysis and interpretation of high resolution X-ray spectra using a spectroscopy database such as the ATOMDB. It is a stand-alone, programmable and extensible S-Lang-based system.
A variety of fitting modes are provided to support simple line profile fits as well as global fits; a pileup model for CCD spectra is also included (this is also available in Sherpa as the jdpileup model).
See the ISIS webpage for more information and download instructions.