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.
Would you mind giving an update on your project? I must have missed the later post you're mentioning above. It might be interesting both for you and your future clients if you could sketch how you would handle core issues of Futures, settling, margining, matching? I'm sure many of us have pet hates about existing exchanges and how they deal with their users. Taking early feedback on board might prevent repeating mistakes certain exchanges or market data providers keep making over and over again.? I'd appreciate any information you can share, maybe an early prototype for testing the idea?