Central server that maps did:plc identifiers to their DID documents — widely and rightly criticized as the single most centralized element of the AT Protocol network. 'PLC' was originally 'placeholder' and was later retconned to 'public ledger of credentials'. An export API returns batches of up to 1,000 operations on DIDs, which developers use to track handle changes (e.g. Kuba's handle-TLD statistics). Bluesky announced at atmosphere conf (the month before the talk) that they have funded a separate organization in Switzerland to manage the PLC directory independently.