ULySS (University of Lyon Spectroscopic Analysis Software) is an open-source software package written in the GDL/IDL language to analyze astronomical data. ULySS fits a spectrum with a linear combination of non-linear components convolved with a line-of-sight velocity distribution (LOSVD) and multiplied by a polynomial continuum. ULySS is used to study stellar populations of galaxies and star clusters and atmospheric parameters of stars.
Cite http://adsabs.harvard.edu/abs/2009A%26A...501.1269K and put the URL of the ULySS home page in a footnote. If you use the SSP models, also cite http://adsabs.harvard.edu/abs/2008MNRAS.385.1998K.