Make Your Market looks interesting. Seems like it lets you create hosted exchanges very simply, with access via FIX.
Make Your Market provides its users with a new approach to trading, allowing them to create a full featured market with their instruments and their community of participants to trade. Make Your Market provides its users with a full featured real-time web front-end.
* Create market/instrument on the fly
* Perfect solution for spread betting
* Positions management, risk management, order book overview
* Fully MifiD and FIX compliant
* Easy integration with clearers and brokers
* Possibility to link to real markets
* Using the latest web technology, access from any location
* Fully hosted solution available
* Easy integration into existing architecture
* Easy white labelling