MatterControl - MatterControl is a free, open source app that lets you organize and manage your 3D prints.
STP Viewer - Free STP Viewer - free software that lets you view 3D STEP files (.stp, .step file format).
Slic3r - STL-to-GCODE translator for RepRap printers Here comes Slic3r! Its features are: - speed
A360 VIEWER - Free online CAD Viewer
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
DXF View - A lightning-fast drawing viewer enables you to view DXF and DWG™ files on Mac