The idea behind NFTs is that they are unique digital items and their uniqueness means that they can be traded as assets. However, this could lead to a situation where someone creates an NFT that you don't want and assigns it to a sat that's already in your wallet. To prevent such situations, the email suggests using zero-knowledge proofs that make it impossible to associate who received bitcoin with who spent it. However, off-chain colouring provides a way around this solution. Someone can create an NFT that you don't want and assign it to the same ordinal/sat as some existing NFT that you do value. At this point, it's presumably impossible to discard one without discarding both. This can be done by writing a patch to ord and composing a nostr message.The writer proposes a simple NFT system that references an NFT (whether real or electronic) by an initial hash, which is then given a final reference as the hash of the initial hash. The real owner must prove that they have knowledge of the initial hash to prevent theft or counterfeiting. The NFT owner references the NFT signed by them in some trusted third party allowing a timestamp. A thief cannot intercept the "minting" transaction and steal the NFT or do/replay a transaction with this NFT, minting it or selling it several times.Then, the NFT owner and buyer exchange information like for lightning and do one transaction on Bitcoin storing the deal. The continuation of this proposal is "A Universal Coin Swap system based on Bitcoin." Anthony Towns shares his idea of moving inscriptions entirely off-chain, allowing all the "inscription" data to be entirely off-chain. The only thing that requires a transaction on-chain is transferring ownership to someone else.He suggests creating an asset off-chain and associating it with an ordinal. This allows NFT's existence to be kept entirely private if desired, makes it cheap to create a new NFT, and doesn't impose an outsized overhead on people who aren't interested in your inscriptions but may be interested either in bitcoin per se or in other inscriptions.He believes that comparisons to ordinal inscriptions aside, there is another interesting point from all this. Presume you have a tool that implements the nostr ordinal assignment suggested above: that is, a small modification of the "ord" tool that can track a chain of custody for an ordinal specified in a nostr event like above. That allows you to do NFTs completely unobservably -- you don't have to publish anything to the blockchain apart from ordinary looking transactions to transfer ownership of your NFT.The email also mentions that Liquid's multi-asset model may be superior to NFTs, particularly for semi-fungible tokens. In Liquid's model, if you have a utxo with 1M sats, 500 of which are inscribed to each represent rights to $1 worth of USDT, then rather than acting like a stable coin and being worth $500, it's actually worth $500+0.01BTC, which is more like $750 and changes as the value of bitcoin changes.The author of the email, Aymeric Vitte, has included links to various projects he has worked on, including a universal coin swap system based on Bitcoin, a bitcoin NFT system, a tool for moving coins by yourself, a project for simplifying Bitcoin transactions, and others.