The problem Cross Chain Identity (NFT Delegation) solves

The primary motivation is to leverage each blockchain storage by allowing users to log in with an account at any dApp and see all the NFTs owned in different blockchains. It uses soft delegation, meaning you need to be connected to only one blockchain. E.g., If my FLOW address: 0xNachoFlow has 10 NFTs, I can set a delegation to my Ethereum address: 0xNachoEVM. Therefore, I can join Metaverses like Decentraland, Marketplaces like OpenSea, etc., using 0xNachoEVM and see EVM NFTs and the 10 NFTs owned in the FLOW blockchain by 0xNachoFlow.

The POC is using @ethereum and @flow, but it can be any. The (ugly) UI to play is identity-nachomazzara.vercel.app. Transactions in Flow using @blocto are free, and for Ethereum, you need to be connected to Goerli, but the NFTs will be fetched from OpenSea API, so it will retrieve NFTs from every EVM blockchain supported there. To fully use it, you may need to have NFTs in Flow and Ethereum. After delegating to the desired address, you can then connect with that delegated address and see all the NFTs displayed together.

Challenges I ran into

Learn Cadence. New paradigm from objects to resources. Set up things to send txs in Flow. Use public NFT Flow projects API