The growth of alternative trading systems competing with traditional stock markets has been a phenomenon in financial markets over the last decade.  The Financial Times has a nice article on the competition in Europe from these new marketplaces, claiming they typically compete on  speed, capacity and cost.   As it happens, they also compete on anonymity and confidentiality.  Some platforms even allow a trader not to decide whether to buy or to sell a stock until the counter-party reveals his or her hand.
But on speed, the results are impressive:

“On Chi-X’s system, a trade can be executed in two milliseconds, compared with about six on the LSE [London Stock Exchange].  The blink of a human eye takes about 200 milliseconds.”