Files with the CO extension are mainly created by CAD / CAM software called Cobalt 3D. It is a professional software tool for 3D computer modeling. It was released for Microsoft Windows and macOS.

CO is a file used to store projects made in Cobalt 3D. It is a format specially developed for this program and it is proprietary. This solution allows the authors of projects to exchange works, as well as to save unfinished works for later editing.