VLM

VLM is the format used for 2D and 3D drafting files in Vellum from Ashlar-Vellum, which later became Graphite and used VC6 files.

Software
A free viewer can be downloaded in the publisher's site, for Graphite but will also view Vellum files.

Links

 * Graphite page in publisher's site
 * Wikidata: Ashlar-Vellum