I can't tell if people don't understand how financial firms work or are you just being sarcastic.

If a company has customers, and those customers buy a product, the company charges a price for that product.

> If a company has customers

They don't...

a) What do you call this at the bottom of the page https://www.hudsonrivertrading.com/liquidity/

b) If you don't have customers, why have a company?

I don’t really understand question b), how else would you organize a venture involving more than a couple people?

I think you're misunderstanding what that page is: it's not an advertisement to invest with the company, it's an advertisement to trade via/with the company in the same way you might otherwise go manually trade from a Bloomberg terminal (or any other method).

There is no way to invest in the company, and the only way of becoming a "customer" is to engage in trading.

They're a market market that provides liquidity to clients. They (as far as I know) don't charge fees, but earn their profits by exploiting the ask/bid spread.

A customer might want to offload TSLA and are willing to pay the market rate of $329. This trade might work in HRT's favor if they can sell it for $329.01. It's just 1 cent, but over millions of transactions these small amounts of profit add up.

The value captured by HRT is meaningful in the aggregate, but tiny and irrelevant to the institutional clients, and therefore can't be thought of as a fee. What HRT provides in return for taking clients' trades is liquidity.