Hi! I'm Casey Rodarmor, very very minor ex-Bitcoin Core contributor, current host of the SF Bitcoin Devs meetup, and full-time ordinal theory researcher.
Ordinal theory has two main branches, ordinal numbers, and inscriptions.
Ordinal numbers are a scheme for assigning serial numbers to sats and tracking them across transactions. This is done without any on-chain data, is entirely opt in, and don't affect fungibility.
Inscriptions attach on-chain content to sats, creating digital artifacts that
then be tracked and transferred using the ordinal numbering scheme. These
digital artifacts, just like sats that they ride on, can be contained in a
normal bitcoin UTXO, transferred using normal bitcoin transactions, and sent to
normal bitcoin addresses. This requires a wallet that performs sat control,
Inscriptions are NFTs, but the term NFT feels tainted, so I coined the phrase "digital artifact" to try to express what inscriptions aim to be. Inscriptions are on-chain, secure, immutable, and uncensorable, unlike NFTs which are often off-chain, insecure, and riddled with weird caveats.
Ask me anything about ordinals, inscriptions, SF Bitcoin Devs, Bitcoin, or anything else!