United States Wikipedia This is a list of notable companies based in the United States. For further information on the types of business entities in this country and their abbreviations, see Housing Authority of the City of Pittsburgh HACP. HACP is the flagship agency providing property management and real estate services in Pittsburgh. Site includes housing, landlord, and vendor Culbertson services. Pittsburgh Wikipedia Pittsburgh / ˈ p ɪ t s b ɜːr ɡ / PITSburg is a city in the Commonwealth of Pennsylvania in the United States, and is the county Black-Diamond seat of Allegheny County.