The Sporting Exchange (the owner of the BetFair brand):

Betfair is the world’s leading online betting exchange, a concept it has pioneered. [1] Driven by cutting-edge technology, Betfair enables punters to choose their own odds and bet against each other, even after an event has started. Betfair processes 5 million transactions a day and more than 300 bets a second.

In addition to the exchange, Betfair has an established games portfolio. Betfair Games, which includes Betfair Poker, is hosted from Malta and is an area which has seen significant growth and investment. The company is also developing new revenue streams by providing automated price feeds to third parties, establishing white-label exchanges and through its own Betfair Mobile product.

Launched in 2000, Betfair is a profitable and debt-free company with annual revenues exceeding £140 million. It is a privately-owned company. Betfair is proud that a large percentage of its employees own part of the company through its SAYE scheme.

[1] According to Paul Rhode and Koleman Strumpf, prediction markets in New York organized trading on  the 19 elections that took place from 1868 to 1940. (PDF)

And the Iowa Electronic Stock Market was created in 1988.