LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
AutoCAD MEP - AutoCAD MEP software helps you draft, design, and document building systems.
QCAD - QCAD is an application for computer aided drafting in 2D.
DataCAD - DataCAD is a computer-aided design and drafting software for 2D and 3D architectural design and drafting
FreeCAD - An open-source parametric 3D modeler
AutoCAD Plant 3D - AutoCAD Plant 3D is a BIM software that lets you create, modify, and manage schematic piping and instrumentation diagrams.