Fei Protocol is a DeFi-based stablecoin that aims to provide a balance between overcollateralized decentralized stablecoins and centralized custodial stablecoins. It operates with two crypto assets, FEI stablecoin and TRIBE governance token. The goal of FEI is to be a fully decentralized and capital-efficient stablecoin, using the value it controls to maintain liquidity and earn yield for the protocol.