Augur was one of the first ICOs. They promised a decentralized oracle and prediction market protocol (with dispute resolution) and that's what they delivered.

Their REP token sale was in 2015, they spent a few years developing their smart contracts while providing weekly updates and contributing a lot back to the Ethereum community, and finally launched in July 2018.

https://www.augur.net/

https://augur.stackexchange.com/

To see the prediction markets without setting up the Augur client, you can use the following site:

https://predictions.global/