Unity - The multiplatform game creation tools for everyone.
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.
Godot Engine - Feature-packed 2D and 3D open source game engine.
Autodesk Design Review - Design Review lets you view, mark up, print, and track changes to 2D and 3D files.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
ZWCAD Viewer - Cross-Platform .DWG | .DXF | .DWT R12-2013 Viewer