XOP 2.1 - A New Version of the X-ray Optics Software Toolkit Manuel Sánchez del Río[1] and Roger J. Dejus[2] 1) European Synchrotron Radiation Facility, BP 38043 Grenoble-Cedex, France 2) Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA Abstract. X-ray oriented programs (XOP) is a graphical user-interface environment for computer codes of interest to the synchrotron radiation community. It provides codes for i) modeling of x-ray sources (e.g., synchrotron radiation sources, such as undulators and wigglers), ii) calculating characteristics of optical elements (mirrors, filters, crystals, multilayers, etc.), and iii) multipurpose data visualizations and analyses. The current version of XOP (2.0) has been widely distributed at synchrotron facilities and research laboratories. It can be downloaded from http://www.esrf.fr/computing/scientific/xop, and it is also distributed on a CD-ROM. Today, we count over 400 registered users. We describe recent developments including improved documentation and user interface, and upgraded applications. The functionality of XOP can be extended with external plug-ins (extensions). We continue to support a visual interface to the SHADOW ray-tracing program and the multilayer package IMD