The common name for Ammonium carbonate, which comes as a colorless-to-white crystalline solid and also sometimes known as aromatic spirits of ammonia.
The reason smelling salts have the effect on people that they undoubtably do is the ammonia fumes from the compound irritates the membranes of the nose and lungs, which triggers an unconcious reflex causing the muscles that control breathing to work faster. This has the obvious upshot of increasing oxygen volume in the blood.