There are many companies registered as brokers with FINRA, although some may use their broker designation for different purposes than others. Many proprietary trading firms are registered as brokers so that they and their traders can directly access trades, but they do not offer broker services to customers in general. This is distinct from the role that discount or full-service brokers might provide.
Full-service brokers tend to use their brokerage role as an ancillary service available to high net worth clients in conjunction with many other services such as retirement planning or wealth management. Examples of full-service brokers might include offerings from a firm such as Morgan Stanley or Goldman Sachs or even Bank of America Merrill Lynch. These firms may also use their brokerage services on their own behalf or on behalf of corporate clients to make large transactions in equities.
Other full-service brokers may offer specialised services including trade execution and research. Firms such as Cantor Fitzgerald, Piper Jaffray, Oppenheimer and others. There are many of these firms even though their ranks have dwindled due to mergers or the increased costs of complying with regulations such as the Dodd Frank Act.
Still other full-service brokers offer advice and personalised communications with clients to help manage assets and plan for retirement.
Most of the larger brokerage firms tend to keep an inventory of stocks available for sale to their clients. They do this to help reduce the cost of exchange commissions, but also because it allows them to offer quick access to popular stocks. Other full-service brokerage firms are actually agency brokers. This means that, unlike many larger brokers, they do not have stock inventory, but act as agents for their clients to get the best trade executions.
Many discount brokers have made a significant change in their business model that included no commissions on some or all of their stock trades. Examples of some discount brokers include Fidelity, Charles Schwab, E-Trade, Interactive Brokers and Robinhood.
Proprietary trading firms registered as brokers may not advertise their services as brokers, but use their broker status in a way that is integral to their business. While banks or larger firms may have proprietary trading desks within their company, a dedicated proprietary trading firm tends to be a relatively smaller company.