The download has been started, click here if it doesn't start automatically.
After download, open the .dmg file and drag the 3D Model Viewer.app to the Applications folder.
Then, open the app to load any 3D model file, or open a file in the Finder to preview it.
The supported extensions are same as on this website.
After download, open the .msi file and install the application by following the instructions.
Then, open the app to load any 3D model file, or open a file in the File Explorer to preview it.