BRL-CAD is an open source cad systems based around constructive solid geometry (csg) modeling. On top of all of it's modeling features, such as the interactive geometry editor, BRL-CAD offers parallel ray-tracing, path-tracing, image and signal processing tools. The ray-tracing process can even be distribution over a network of computers. When starting a new model determining an accurate unit of measurement ensures that your models will always have the correct proportions compared to real world objects. CSG is a fascinating way to work with 3d modeling and allows you to quickly build rough models and can be finalized later with all required details.

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 primarily 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". It does also support boundary representation.

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 ray tracing 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.