Wikipedia
BRL-CAD is a constructive solid geometry (CSG) solid modeling computer-aided design (CAD) system. It includes an interactive geometry editor, ray tracing support for graphics rendering and geometric analysis, computer network distributed framebuffer support, scripting, image-processing and signal-processing tools. The entire package is distributed in source code and binary form.
Although BRL-CAD can be used for a variety of engineering and graphics applications, the package's primary purpose continues to be the support of ballistic and electromagnetic analyses. In keeping with the Unix philosophy of developing independent tools to perform single, specific tasks and then linking the tools together in a package, BRL-CAD is basically a collection of libraries, tools, and utilities that work together to create, raytrace, and interrogate geometry and manipulate files and data. In contrast to many other 3D modelling applications, BRL-CAD uses CSG rather than boundary representation. This means BRL-CAD can "study physical phenomena such as ballistic penetration and thermal, radiative, neutron, and other types of transport"
The BRL-CAD libraries are designed primarily for the geometric modeler who also wants to tinker with software and design custom tools. Each library is designed for a specific purpose: creating, editing, and raytracing geometry, and image handling. The application side of BRL-CAD also offers a number of tools and utilities that are primarily concerned with geometric conversion, interrogation, image format conversion, and command-line-oriented image manipulation.