APEC: Astrophysical Plasma Emission Code
Code to predict spectra for collisionally ionized plasma in the optically thin limit. It is a replacement for the 1970's Raymond-Smith code. The APEC FITS output files maintain individual information on all strong emission lines, continuum, and pseudo-continuum from many weak lines. Using APEC on the APED will produce the ATOMDB. See the ATOMDB website for more details on APEC.
APEC is available within Sherpa as the xsapec model.