Commons now supports the uploading of 3D objects in the STL file
format. 3D files will show a static preview image when viewing, and an
interactive viewer will load when that preview image is clicked.
To upload a 3D file, log in (or create a new account) and click the
“Upload file” link on the left of the page. When viewing 3D files,
please make sure you have the MediaViewer enabled to use the
interactive 3D features.
Please help us test the feature and upload your 3d objects. There are
a few bugs the team is tracking. Please ping me if you need help
filing a Phabricator task.
For more information on the feature, you can read he help
documentation and the technical documentation on how the MediaWiki
extension works.  
The first object to be uploaded is a 3D model of a Asad Al-Lat statue
that was destroyed in the ancient city of Palmyra, Syria along with
most of the main world heritage ruins in the city.  The image is
tagged with #NEWPALMIRA in honor of Bassel Khartabil. 
You can search for all uploaded 3D objects by using "filetype:3d" in
your searches. 
There is also a Wikimedia blog post announcing this to the rest of the
world. :)