LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
NttCAD - Free 2D/3D CAD software, easy to use and multi-platform
Piglet Drawing Editor - 2-D engineering drawing editor that supports hierarchical object description
TYCAD - TYCAD is a application for computer aided drafting (CAD) in two dimensions (2D).
QCAD - QCAD is an application for computer aided drafting in 2D.
DraftSight - Discover Dassault Systèmes®' DRAFTSIGHT™ Professional CAD software that lets you create, edit, view and markup any kind of 2D drawing. Learn more here.