Is there any common trading system that is implemented by hedge fund, especially for equity or forex automated trading? I know some big names like Sungard and Bloomberg. Is there any other choices which the including API?
Bloomberg: TOMS, SSEOMS, AIM, EMSX
TT Trading Systems (X-Trader, mostly for futures, spreads,...)
Orc Group: Orc (often used for listed options)
And uncountable others, really depends on which product you look to trade.
But please note that you asked specifically about automated trading and to be honest, most shops code up their own order execution platforms and hook them up to Fix adapters or APIs of brokers, banks,...
You might want to take a look at the Waters Technology buy side technology awards, especially for execution management systems (EMS). Most hedge funds want to use multiple counterparties so they would want a broker-neutral trading system. As far as I'm aware, the most popular platforms are Portware and Flextrade.
Disclaimer: I work for AlgoTrader.
AlgoTrader is used by some smaller hedge funds, especially in the volatility trading area.
AlgoTrader is a Java based Algorithmic Trading Platform that enables development, simulation and execution of multiple strategies in parallel. The automated Trading Software can trade Forex, Options, Futures, Stocks & Commodities on any market. The system is based on Complex Event Processing (CEP) and Event Stream Processing (ESP) using Esper.
Also, the system does have both a FIX interface as well as Bloomberg connectivity.