Rayspace has been around for a while, yet I have not seen it reviewed or much talked about. It is a 'Space Design' type reverb, allowing the user to create a room or space visually, and then synthesize its reverb characteristics using ray tracing techniques.
The UI is very clean and straightforward in typical Quikquak style. The space in use can be viewed and edited in an overhead mode (where you can also 'see' the actual paths traced by the rays if you wish) and also in a 3d mode to aid visualisation. Pretty much all parameters of air and surface can be adjusted, as well as the positions of sound sources and listeners.
The number of 'rays' can be adjusted to control the density (and CPU use).
The sound is clean and reasonably free of artifacts, although the longer tails are not as smooth as some more recent algorithmic reverbs. It is interesting that multiple modes of reflection are clearly audible, giving the result a very complex but still well defined character. The controls allow results from subtle (where it works best, I think) to ridiculously over the top.
The feature set is good and a wide variety of spaces can be successfully modelled. Most parameters can be automated, including source and listener positions. As a FR for future versions, the option to pan from the dry signal in synch with the reverb would be useful.
There is no manual provided. Good help is available on the GUI and it is all you really need but a pdf to keep on the desk while learning wouldn't go astray.
Presets are numerous and very well illustrate the range of possibilities this plugin offers.
I have had a couple of occasions to contact QQ support and they are just the best. Prompt and useful replies to eMail and I am sure they would not rest until any problems were ironed out. Full marks here. It has been solid as a rock (Win7 64bit, Energy XT2.5).
VFM? As a general purpose instrumental reverb, there are many freebies out there that sound as good or better, so this is not for that. But if you like the visual approach (I do), or if you think in terms of shapes and spaces then check this out. Also, it is great for designing spaces that are not of regular shape or acoustic properties. If you do foley or make FX or audio post for radio, music or video, then Rayspace lets you cobble up soundspaces in no time flat. For these applications, it is a bargain.
edit: The final reverb characteristic impulse can be exported as a wav file and imported into a convolution reverb / IR loader. Beware, some of these wav files can be quite large.