Any System trading softwares or brokers offering API

I am looking for any system trading software or any broker offering APIs to develop system trading sw.
Can someone help me on that

What is a system trading software? Can it create its own rules and work without any charting s/w? In that case it should be able to place trades directly to the platform, isn't it?
a lot of sexy and excellent one are available free on google ...

Zerodha – Open Paperless Account

Open online account with Zerodha. Free delivery trading and Max Rs 20 for Intraday, F&O, Currency and Commodity Trading. Intraday High leverage with MIS, CO and BO.

Are you a day trader?