The Ethereum network has a special type of token called ERC-721, which is used for non-fungible tokens (NFTs). These NFTs are unique digital assets that can represent anything from art and music to virtual real estate and collectibles. One of the most famous examples of an NFT project on Ethereum is CryptoKitties, a game where players can breed and trade digital cats. At its peak, CryptoKitties was so popular that it congested the Ethereum network, significantly increasing transaction times and fees!