There was a company called Zecco (zecco.com) which also did something similar with zero commissions (hence the name). Not sure if they're still active.
Update: looks like they (zecco) were bought by tradeking.
So from the FAQ Page it looks like they will make money from margin accounts (presumably swap/interest) and also by charging for API access.
It was developed and designed in Denmark by an agency i co-founded and then incorporated in the US a year later.
They merged with TradeKing a couple of years ago.
The intent with ZEro Cost COmmission was to be free and making money on margin accounts. But as I think these guys will find its going to be tough to build a business on that.
As circumstances will have it I am having lunch with one of the original zecco people today :)
http://www.russellbeattie.com/blog/artisanal-websites-the-ri...
(Beattie credits evocative short name, stable British administration, lots of available short and English word domains.)
Another clever new-ish one is .ac, but it's more expensive than the already expensive .io.
.io domains are very popular in a ton of different areas, though!