It's not exactly on-topic for this thread, but just for reference I'm working on a full featured futures contracts trading system (intraday, marginal trading, market making, interface for algorithmic traders). If there is such a demand, prediction market could be supported as well, however I specialize only in serious financial stuff and derivatives markets.

I will make more posts about this later, with a more thorough description. If there are any suggestions/etc - please feel free to discuss.