Where are the best opportunities for an experienced independent software developer with his own small company in the API interfacing space? These could be new extensions of trading platforms that I would develop and market, or else possibly custom development services. For example, possibilities might include: -TradeStation extensions or strategies -Trading Technologies XTrader custom extensions -CTS T4 extensions and customization interfaces -QuantHouse custom implementations -CQG and others I am not looking for work developing for any of these API's right now, but rather looking to determine which API would be most useful for me to get intimately familiar with on my own over the coming months to a year, with a view to eventually developing and selling either products or (as second choice) services through my own small company. I have already developed some code for the CTS T4 and Interactive Brokers API's, as well as for TradeStation, but am wondering if XTrader and QuantHouse, for example, might be much richer markets to enter. Any comments are welcome.