ORD-721 was started around the same time when BRC-721 was started, about 3 months ago.
Differences are mostly technical, and that BRC-721 is promoting off-chain data. Ord-721 support both off-chain and on-chain, but recommending on-chain. It's easy to add a "fallback" link image to HQ but you should at least own/have some content.
Neither are visible on the ord wallet, or on other wallets and marketplaces, for now.
Ord721 has more structure and can define many things on the Collection Manifest inscription - which plays as the source of truth for a collection. Things like name, description, max supply, mint price, and optionally royalties definition, website, twitter and etc stuff if creator decides. Brc721 doesn't support much of that, at least such things won't be on the collection definition.
Each item of a collection is called Token Manifest, in which both the content (image, svg, html, or anything), and the metadata (like traits/attributes, and token id) are in one place - the content inside token.uri and the metadata in token.traits (key-value object) or token.attributes (array of objects, 1:1 with what we see on erc721 attributes). So the user actually owns everything and it doesn't depend on centralized storage or on the choice of a creator to insclude or not your item in a collection.
Ord-721 do not have reveal mechanics. Intentionally. It's a feature, not a bug. It's still possible though.
People that trade Brc721 are trading nothing more than just a plain json file with no value, which don't actually contain anything about the image, the attributes, token id, or anything. It just verified that it's part of some collection, because at least it contains the collection's inscription id. But that's all. You cannot manually check (by following links in platforms like marketplaces) or verify what's the actual content/image, because there's no link/pointer to the so-called "Reveal Manifest". Example is the Ordinal Dooms on Magic Eden. You see some image there, if you check the content of the given inscription, ti doesn't contain the image or link to the image.
Ord721 is easier to integrate in wallets and marketplaces that listen on Ordinals indexer inscriptions. They just need to detect the protocol, an show the contents of the token.uri - which can be a link (meaning the item is off-chain), or just raw dataURI base64 of the content. Having collection pages is easy too - they can just get all the info from the Collection Manifest inscription.