From some of the comments I see, let's not read too much into this. He's not asking how to build an -automated- trading system, just one that's realtime and al

From some of the comments I see, let's not read too much into this. He's not asking how to build an -automated- trading system, just one that's realtime and all analysis and decisions are made by the user. The best I've seen that's commonly available is "Trader Workstation" and it's free with your account at Interactive Brokers. It's written in Java.