tradestation is more than just an online brokerage. alot of their revenue comes from their trading software as well feed data, which, if memory serves me correct, is how they started. they used to be very popular among active traders, in particular because of their charting, scanning, systems and back testing software...but there are now a handful of other companies that offer equivalent, if not better bargains on the software front.
Market Data 
Markets 
AI
