LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Piglet Drawing Editor - 2-D engineering drawing editor that supports hierarchical object description
TigerCad - A completely free, simple technical drawing software (CAD)
QCAD - QCAD is an application for computer aided drafting in 2D.
A9CAD - 2-dimensional CAD program supports industry standard DWG/DXF drawing formats
DraftSight - Discover Dassault Systèmes®' DRAFTSIGHT™ Professional CAD software that lets you create, edit, view and markup any kind of 2D drawing. Learn more here.