u-he protoverb

Protoverb is an experimental reverb based on the idea of a "room simulator". Most algorithmic reverbs try to avoid resonances or model the reflections of sound from a rooms walls. Protoverb does the opposite. It builds up as many room resonances as possible, modeling the body of air in the room. It therefore does not need to modulate or colour the signal. The result is a very natural sounding reverbration with some interesting features: Long standing frequencies resonate louder, as if the air takes some time to get excited. Multiple instruments don't mash into a diffuse mud, they stay distinct. If you play a short melody, the room seems to repeat a ghost echo of that melody. Those properties are indeed found in churches and large halls, but they're rarely found in conventional algorithmic reverbs.

http://www.u-he.com/cms/179-protoverb