What are some alternatives?
When comparing JustCAD and QCAD, you can also consider the following products
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.
FreeCAD - An open-source parametric 3D modeler
Draft it - Draft it is a CAD software package that allows to create, save, & print work with drawing tools that allows to create professional drawings for project.
TigerCad - A completely free, simple technical drawing software (CAD)
nanoCAD - nanoCAD is a pro-grade 2D CAD system with native DWG support and full customizability.