Augur, developed by the Forecast Foundation founded in 2014 by Jack Peterson, Joey Krug, and Jeremy Gardner, was the first decentralized prediction market and one of Ethereum's earliest projects. It pioneered the trustless, user-created market model and an on-chain oracle for resolution.
High Ethereum gas fees historically made casual trading expensive, and a later move to Polygon ("Augur Turbo") came after Polymarket had captured the market. Today Augur is more influential as a template than as an active venue, but its technical legacy runs through much of the DeFi prediction space.