FreeCAD - An open-source parametric 3D modeler
nanoCAD - nanoCAD is a pro-grade 2D CAD system with native DWG support and full customizability.
OpenSCAD - OpenSCAD is a software for creating solid 3D CAD objects.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
DraftSight - Discover Dassault Systèmes®' DRAFTSIGHT™ Professional CAD software that lets you create, edit, view and markup any kind of 2D drawing. Learn more here.