AutoCAD is widely used commercial software for 2D & 3D Computer Aided Designs (CAD) and drafting. It allows users to bring to life basic geometry and is great for drawing precise line work, such as elevation details.
Revit is a Building Information Modelling (BIM) software for architects, engineers, contractors and designers. It can create a unified model that contains real-life information. It is great for modeling, clash detection, and change management.