BRL-CAD is a collection of tools for assisting with Computer Aided Design and has been actively developed by the U.S. Army Research Laboratory since 1979. As a Constructive Solid Geometry (CSG) modeling system BRL-CAD supports full interactive 3D editing and has a high performance ray tracing engine. Amongst its other features are network rendering support and a scripting language.

BRL-CAD has a good collection of tools for creating drawings and includes one of the fastest raytracing engines around, has the ability to use a network for speeding up rendering and also features it's own scripting language.

BRL-CAD has been used by the US Military for more than 20 years for weapons systems modelling amongst other things. BRL-CAD has also been picked up by academic institutions and being used for industrial applications.

BRL-CAD was originally built for Unix systems and that remains true today with its support for Linux and OS X. Although there also recently a Windows version available.