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.
FreeCAD - An open-source parametric 3D modeler
AutoCAD Arch - Design and document more efficiently with the AutoCAD Architecture toolset, created specifically for architects.
gCAD3D - 3D - CADCAM - Software for MS-Windows and Linux. Freeware
AutoCAD Plant 3D - AutoCAD Plant 3D is a BIM software that lets you create, modify, and manage schematic piping and instrumentation diagrams.