Autodesk's original 2D/3D drafting software - the industry standard for decades before BIM, and still the tool most Revit newcomers are transitioning from. The core mental shift moving from AutoCAD to Revit is that CAD draws independent lines representing a wall, while Revit models an actual parametric wall object that generates those lines (and every schedule, section, and quantity) automatically - which is why "AutoCAD habits" like manually drafting details from scratch are the most common source of friction for new Revit users.