Vladimir Sadovnikov has released the free room builder plugin LSP Raumbaumeister Stereo.
This plugin allows to simulate impulse response of any modelled room or space. The basic principle is based on generating of unit audio impulse and then capturing all it’s reflections from environment by special capturing objects that simulate microphone capsules.
So, in fact, this algorithm is a kind of raytracing algorithm but instead of single rays it performs tracing of ray groups. This allows to simulate large spaces withous significantly loose in quality and precision.