Bitcoin Builder started out as a way to trade against MtGox's internal ledger when they halted withdraws. Users could effectively bet on MtGox's future by using

Bitcoin Builder started out as a way to trade against MtGox's internal ledger when they halted withdraws. Users could effectively bet on MtGox's future by using privately held bitcoins to trade with users wanting to sell their "Gox coins" at a fraction of the market price. Anyone that sold their Gox coins for less than 100% market value made out far better than those that didn't. It was a wild idea that basically created a functional market for the greedy and the desperate. I'm sure millions flowed though the site during its short lived existence. Congrats on the new idea, Josh.