This is a Blender add-on that allows importing and exporting 3MF files.
3D Manufacturing Format files (.3mf) are a file format for triangular meshes intended to serve as exchange format for 3D printing applications. They can communicate not only the model, but also the intent and material of a 3D printing job from the CAD software to the CAM software (slicer). In this scenario, Blender serves as the CAD software. To that end, the aim of this add-on is to make Blender a more viable alternative as CAD software for additive manufacturing.
Since the add-on catalogue wiki pages are archived, instead here is a link to a page with full info, including usage instructions and documentation of all features (as suggested to me by developers): https://github.com/Ghostkeeper/Blender3mfFormat/blob/master/README.md
This add-on has been tested by a number of friends initially, but has recently gained traction in the community. It appears to be quite stable. I'll start with submitting it as a community release but would be fine with it being included in official releases too.