McXtrace - Monte Carlo ray tracing simulations of X-ray experiments.

McXtrace is a tool for simulating X-ray instrumentation and experiments using a
ray-tracing formalism. Currently the main use of McXtrace is in the field of 
synchrotron beamline instrumentation design, but various other uses have been 
found, such as designing X-ray telescopes or for laboratory source-based
equipment.

WWW: http://www.mcxtrace.org