SpatialVerb is an open source plugin that uses raytracing to generate a realistic early impulse response. You can control the size of the room, location of two virtual source speakers and two destination microphones.
The late impulse response is governed by a Circulant Feedback Delay Network (CFDN) which in contrast to many other reverb filters has a very low amount of ringing. You can control the FDN by setting feedback, cutoff and gain. You can adjust the feedback and gain of the FDN so that it's response is a natural progression from the early response of the room.
