Independent regulatory commissions are not under the jurisdiction of the president. They have three to five or more commissioners or board members with equal votes, are confirmed by the Senate and serve fixed terms, typically four years. Government Corporations exist in a nether world. Typically they started out as a government agency, often during the New Deal, but since then have been given autonomy. Their functions are like a business, but for the most part they do not seek to make a profit.
Central agencies direct or provide service to the entire national government.