

If 404's are fractional, then they would presumably be similar in a way to a regular token. So what are the core differences between 404's and erc20's?

Essentially ERC404 is a combination of ERC20 and ERC721 (NFT).
When you purchase a whole token (ERC20) you will also receive an nft (ERC721).
This mechanism actually solves the liquidity problem of traditional NFTs, since it ties them to a token with a liquidity pool (tradable at any time).
This is the future my friend.
We have written a full explanation here https://musing.io/c/404