OpenSea is the world’s first and largest web3 marketplace for non-fungible tokens (NFTs) and crypto collectibles, launched in 2017 by founders Devin Finzer and Alex Atallah. It provides a decentralized platform for users to create, buy, sell, and trade NFTs, including digital art, music, virtual land, and more, across multiple blockchains like Ethereum, Polygon, and Solana.