Quote from silicon.bz:
This looks grand, but who can I connect this engine to? Where does the funding come from? Does there not have to be a brokerage middle-man? It's completing the full picture that I'm having trouble with.
FIX is just a connection protocol, and it is implemented somewhat differently at every place it exists, although the differences can be small.
FIX can be used to talk directly with exchange servers (so no broker between you and the exchange at all), although this type of arrangement, known as "sponsored access", may be tougher to get or even outright banned now, and also requires an expensive exchange colocation.
Many "higher-end" brokers allow you to them connect using FIX, but it often depends on the volume you trade and/or the amount you put in the account. One that will probably give all clients FIX is Lime, but the brokerage itself has certain minima for its clients -- I doubt they'd take someone trading, say, less than 1 million shares per month and with less than $100k opening balance, but I'm not sure about the exact numbers as they're based largely on other posts from ET.
There has to be something else out there