ERC-721 - The Non-Fungible Token (NFT) Standard, was created by William Entriken, Dieter Shirley, Jacob Evans, and Nastassia Sachs due to ERC-20 interface incapabilities. Through an Ethereum Improvement Proposal (EIP) created on the 24th of January 2018.
A popular Ethereum decentralised application, Cryptokitties, utilized ERC-721 to create unique digital collectibles in the form of kitties.
Each different kitten was worth a different amount on the marketplace, dictated by the users of the platform. Each different kitten commands a different price, and as a result, each token needs to be unique.
The creation of blockchain based non-fungible tokens allows for
- physical property (houses, artwork, and vehicles)
- Virtual Collectibles (Cryptokitties, rare pepes, collectible cards)
- Assets with negative value (loans)
In order to create an ERC-721 token, the contract must be compliant with both the ERC-721 and ERC-165 interfaces.