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 Arch - Design and document more efficiently with the AutoCAD Architecture toolset, created specifically for architects.