A sports betting website that uses crowdsourcing to make the best bets. As a user, you predict the outcome of some match, but your final bet isn't necessarily what you chose, but what the crowd data indicates is the best bet.
Much like the CIA found crowdsourcing to be very effective in forecasting global events (http://www.npr.org/blogs/parallels/2014/04/02/297839429/-so-...), I think there's a good chance you could successfully crowdsource things such as betting on sport results.
The way the CIA thing works, I assume (the article doesn't get into much detail), is you have 3,000 people, you ask them to make some predictions, and in the end you select the top 1%. When you compare the future predictions of these top forecasters with those of CIA analysts, you find that the average Joes tend to be more correct (even though they have less information than the CIA analysts).
So you can do something similar with sports betting. You have a group of top forecasters and their predictions for some game assume some probability distribution (like, 30% bet on the home side, and so on). By comparing this distribution with the average odds set by the major brokers, you can identify where the odds have been set incorrectly (according to your crowd) and exploit these weaknesses. For example, let's say that your crowd says that the odds of the Away team winning should be 2:1, but the brokers set the odds at 4:1. Then, this would be a good bet to place, assuming the crowd is 'more right' than the brokers.