ActiveTick, data feed only, works natively on Linux. http://www.activetick.com/activetick/contents/ActiveTickFeedAPIDetails.aspx
Thanks for the link, it seems interesting. It's also cheaper than the competition at $49.95/month for 500 symbols (way more than I need). The only problem with it it's that it looks to be a data feed only. I would also need a routing API that works on Linux, i.e. an API which allows you to send orders to the exchange. Still it's good to know about it.
Actually, they might offer a routing API since they also offer a trading platform. It's definitely worth looking at.
They send the orders to one of these brokers: TD Ameritrade FXCM Gain Capital Forex so routing is available through them. They say other brokers will be available soon.
I thought Active Tick is only for feed. However FXCM and Gain were sued by Gov't for front running their customers, hence I would not trust them. Read this thread, it's very informative, geared towards auto trading Equities on Linux but many of those brokers also deal with Forex. http://www.elitetrader.com/vb/showthread.php?s=&threadid=248841&perpage=6&pagenumber=1
You would not suggest using MONO to work with a C++ API on linux? How do you work with FIX w/o receiving quotes?