It's good easy to learn to use for MEP Drawings Brics CAD can use Cad & BIM extension file DWG # Philemon _Dubai
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Autodesk DWG TrueView - Get a free DWG viewer to view, open, edit, and convert .dwg files, the native file format for AutoCAD files. DWG Trueview includes DWG TrueConvert.
SketchUp - 3D for Everyone
Autodesk Design Review - Design Review lets you view, mark up, print, and track changes to 2D and 3D files.
FreeCAD - An open-source parametric 3D modeler
ZWCAD Viewer - Cross-Platform .DWG | .DXF | .DWT R12-2013 Viewer