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.
- SketchUp site
- Wikipedia article
- Discussion over whether format documentation can be found
- SketchUp: Importing and exporting CAD files
- SketchUp in digital archives. Software and file format analysis and exploration of the options for digital preservation - Report by Henk Vanstappen, commissioned by The Flanders Architecture Institute