Monster Matte is a utility script for 3ds Max from LoneRobot. It lets you browse for rendered backgrounds and set them up as a mental ray matte material, then assign that material to background objects for rendering.
The tool grew out of a production where complex sets had to be consolidated into background renders under tight deadlines. Those shots often needed some form of contact shadow along with masking, which made the mental ray matte material the practical choice. On that production, HD render times dropped from around ten minutes per frame to roughly forty-five seconds, with no perceptible loss of detail or quality.
LoneRobot wrote the utility using HitchHiker, a custom dotnet control, offering it as an example of how built-in dotnet functionality can speed up deploying production scripts. This is version 1. It is listed here as free, and the developer's page at lonerobot.net has the download and any current licensing details.