Freeware - u-he Protoverb 1.0 Reverb VST Plug-In

https://www.u-he.com/cms/179-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.