But, you're right in that there are a bunch of small hedge funds that are operating in this market, too. Still doesn't make it very accessible for those of us without a boatload of money up front to get access.
Professional trading was never cheap. The barrier to entry for becoming a high-frequency trading firm is much, much lower than becoming a NYSE specialist was a decade ago. You could co-locate there for a few million dollars, which is small money all things considered.
Top-5 in LIQUIDITY PROVIDERS, not necessarily the same as in programatiC/algo trading. Goldman tops the list and anyone that's traded on a prop desk knows how much influence they have on the domestic equities market:
But, you're right in that there are a bunch of small hedge funds that are operating in this market, too. Still doesn't make it very accessible for those of us without a boatload of money up front to get access.