Holomatix Rendition is a discontinued raytracing renderer, which is broadly compatible with mental ray.
Its rendering method is similar to that of FPrime in that it displays a continuously refined rendered image until final production quality image is achieved.
It was developed by Holomatix Ltd, based in London, UK.
As of December 2011, the Rendition product has been retired and is no longer available or being updated.
The product is no longer mentioned on the developer's web site, either.