They weren't there to just talk about blockchain, the new technology some predict will transform finance, but to build and experiment with the software.

By the end of the day, they had seen something revolutionary: U.S. dollars transformed into pure digital assets, able to be used to execute and settle a trade instantly. That's the promise of a blockchain, where the cumbersome and error-prone system that takes days to move money across town or around the world is replaced with almost instant certainty. The event was created by Chain, one of many startups trying to rewire the financial industry, with representatives from Nasdaq, Citigroup Inc., Visa Inc., Fidelity, Fiserv Inc., Pfizer Inc. and others in the room.