What project is main rival for Stox? I think that Wings is this one.
But in Stox platform you can make predicitons on differents events, not only "How much money this project will collect".
You can find a comparison with some of our competitors on page 33 of the whitepaper and here
https://medium.com/@fermanto12/stox-vs-gnosis-vs-augur-506997c230dd