There are several NFT standards that define the rules and formats for creating and exchanging non-fungible tokens. Some of the most well-known NFT standards include:

1. ERC-721: This is one of the earliest and most popular NFT standards developed for the Ethereum blockchain. ERC-721 defines standards for creating unique digital assets such as artwork, gaming items, and virtual collectibles.

2. ERC-1155: This NFT standard is also developed for the Ethereum blockchain and allows for the creation of both unique and interchangeable tokens. ERC-1155 provides greater flexibility for creating various types of digital assets, such as in-game virtual items.

3. NEP-11: This NFT standard is developed for the NEO blockchain and is similar to ERC-721. NEP-11 defines the rules for creating and exchanging unique digital assets on the NEO platform.

4. TRC-721: This NFT standard is developed for the TRON blockchain. It provides the ability to create and exchange unique digital assets on the TRON platform.

These standards ensure compatibility and ease of use for NFTs on their respective blockchains, making it easy to create, trade, and store non-fungible tokens.