You might be interested in zipline, an open source backtester written in Python. Zipline, Quantopian's open source backtester (yes, I work at Quantopian).

The backtester is designed to also be a trading engine. You feed zipline data in "events" where each event is a point in time. Zipline doesn't care if the events are live or replayed from a database - it processes the data and executes any trades in the order book.

The tricky part here is that zipline is more aimed at implementing trading algorithms. You'd have to write a simple algorithm to implement the buy/sell orders coming in.

https://github.com/quantopian/zipline