SKP

SKP is a file format used by SketchUp (once owned by Google after they acquired its original developing company, @Last Software, but later sold to a different company, Trimble) for 3D models. It is proprietary and does not appear to have been documented in any publicly accessible place.

Links

 * SketchUp site
 * Wikipedia article
 * Discussion over whether format documentation can be found
 * SketchUp: Importing and exporting CAD files