FeO is used as a black pigment and is known as C.I pigment black 11 (C.I. No.77499) or Mars Black.
FeO is used as a catalyst in the Haber process and in the water-gas shift reaction. The latter uses an HTS (high temperature shift catalyst) of iron oxide stabilised by chromium oxide. This iron–chrome catalyst is reduced at reactor start up to generate FeO from α-FeO  and CrO to CrO.
Bluing is a passivation process that produces a layer of FeO on the surface of steel to protect it from rust.  Along with sulfur and aluminium, it is an ingredient in steel-cutting thermite.