The best free alternative to DraftSight is LibreCAD, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 50 alternatives to DraftSight and many of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to DraftSight are QCAD (Free Personal), BRL-CAD (Free, Open Source), pCon.planner (Free) and Onshape (Free Personal).
Autodesk® DWG TrueView™ software is a free* stand-alone DWG™ viewer with DWG TrueConvert™ software included. Built on the same viewing engine as AutoCAD® software, DWG TrueView enables you to view the latest DWG and DXF™ files, just as you would in AutoCAD.