CAD Assistant is a free desktop application from Open Cascade that lets you open, inspect, and convert professional 3D engineering files — including STEP, IGES, BREP, OBJ, STL, and GLTF formats — without needing a full CAD suite installed.
What is CAD Assistant?
CAD Assistant is a standalone 3D model viewer and format converter built on the Open CASCADE Technology kernel — the same geometry engine that powers FreeCAD, Salome, and dozens of professional CAD packages. On the Mac it lands as a native application that can load the kinds of engineering files that would otherwise require SolidWorks, CATIA, or Autodesk Fusion just to peek inside. I started using it when a client sent me a dense STEP assembly for review and I had exactly zero licensed CAD seats. CAD Assistant opened the file in seconds and let me orbit, section-cut, and inspect every component without dropping a dollar.
What does CAD Assistant do best?
Its strongest suit is faithful, fast rendering of STEP and IGES geometry — the two formats that manufacturing supply chains run on. Most free viewers either mangle B-rep topology or flatten everything into a dumb mesh; CAD Assistant preserves the full boundary-representation tree so you can isolate individual solids, read out precise measurements, and verify that the model is topologically clean before you hand it off to a machinist.
Beyond inspection, the conversion pipeline is genuinely useful. You can batch-drop a folder of mixed STEP, IGES, and OBJ files and export them all to GLTF 2.0 or STL in one pass — which is exactly what you need when feeding assets into a game engine, a web viewer, or a 3D-print slicer that doesn't speak STEP. The output quality is well above what you get from online converters, and nothing leaves your machine.
- Component tree navigation — click any sub-solid in the hierarchy to isolate it instantly
- Cross-section planes — slice the model along any axis to inspect internal geometry
- Measurement tools — point-to-point distances and angles directly on the model surface
- Format coverage — STEP, IGES, BREP, OBJ, STL, PLY, GLTF/GLB, 3DS, and more
- Batch conversion — drag-and-drop multiple files for simultaneous export
Is CAD Assistant free?
Yes — CAD Assistant is free to download and use for personal and commercial purposes. Open Cascade distributes it as a showcase of the OCC Technology kernel, which means you get a production-quality viewer at no cost. There is no freemium gate on file size, no watermarked exports, and no account required. If your needs eventually outgrow a viewer and you want scripted pipeline access to the same geometry kernel, Open Cascade sells commercial licenses to OCC Technology itself — but that's a developer SDK story, not a viewer story.
Who should use CAD Assistant?
Engineers and product designers who receive CAD files but don't own the originating software are the obvious audience. But I've found it equally valuable for a wider circle: 3D artists who receive STEP exports from engineers and need to convert them cleanly to GLTF for Blender or Cinema 4D; procurement teams who need to sanity-check supplier models before kicking off a quote; and developers building CAD pipelines who need a quick visual ground-truth to verify their own converter output.
If you're coming from a pure mesh world — using Blender, MeshLab, or Preview.app to eyeball STL files — CAD Assistant will feel immediately more capable for engineering geometry. It's not a replacement for parametric modelling (you can't sketch or constrain anything), but as a read-and-convert tool it has no serious free rival on the Mac.
What are the best CAD Assistant alternatives?
For pure mesh files (STL, OBJ, PLY), MeshLab is the gold standard on Mac and far more capable for mesh repair and analysis. For lightweight STEP viewing, FreeCAD can open the same formats but brings a full modelling UI you probably don't need just to inspect a part. Autodesk's web-based Viewer (part of the Platform Services) handles STEP and IGES in a browser with no install, which is handy for quick sharing but means your files leave the machine. Hoops Communicator and 3D ContentCentral are enterprise options with licensing costs that make little sense unless you're already deep in a Dassault or PTC ecosystem. For the specific combination of B-rep fidelity, format breadth, and zero cost, nothing on macOS touches CAD Assistant.
How does CAD Assistant compare to FreeCAD?
FreeCAD is a full parametric modelling application; CAD Assistant is a viewer and converter. They share the same underlying geometry kernel, which means both read STEP and IGES with equal fidelity. The difference is intent: FreeCAD asks you to build and modify geometry, while CAD Assistant asks you only to look at it and optionally re-export it. CAD Assistant launches in under two seconds and adds no cognitive overhead. FreeCAD's workbench model is powerful but carries real learning-curve tax. If all you need is to open, inspect, and convert, CAD Assistant wins on every practical dimension.
