- American Simplex - An early American Auto-mobile maker later renamed as Amplex
- Crane-Simplex - American auto-mobile manufacturer.
- Rex-Simplex a German Car manufacturer
- Sheffield Simplex - British car manufacturer from early 20th century
- Simplex of Birminghm - An early British Car manufacturer
- Simplex Manufacturing Corporation - Motorcycle manufacturer
- Also a separate brand of car in Holland, France and Italy
- Simplex chains - brand of roller chain (has become generic for a type).
- Bentall-Simplex - a British Agricultural machinery manufacturer.
- A geometry / mathematical term - see: wikipedia:Simplex
- A Trade name of the British company The Motor Rail and Tram Car Co. Ltd- later Simplex Mechanical Handling Ltd, and now owned by Alan Keef Ltd.
- A French derailleur gear manufacturer used by Peugeot in some of there cycles