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Proof of Authority chains

Chains whose blocks are made by a fixed set of authorities, known by name and admitted by the operator or by a vote of the authorities already in the set. Nobody else can produce a block, and no work or stake is needed to do it: the authorities take turns signing (Clique, Aura), or one proposes and two thirds vote (IBFT, QBFT). Fast and cheap to run, and exactly as trustworthy as whoever picks the authorities.

How it works

Who makes a block	One authority from a fixed set, in turn.
Who may take part	Only the authorities. The set is written into the genesis file or a contract and changed by the operator or by a vote of the authorities already in it. No work or stake is needed; the authority's name and reputation are what is at risk. VeChain also requires each authority masternode to pass identity checks and hold 25 million VET.
How the chain agrees	Clique and Aura rotate signers on a schedule and follow the heaviest chain; Clique lets a signer sign at most one of any N/2+1 blocks in a row. IBFT 2.0 and QBFT have one authority propose and two thirds commit before the block exists.
When a block is final	Immediately with IBFT and QBFT; after a few blocks with Clique and Aura.
What an attack costs	Control of the authorities: a majority of signers on Clique, a third to halt and two thirds to rewrite on IBFT and QBFT. The real check is who appoints them.

What the authorities run

Clique	Go Ethereum's proof-of-authority engine. The signers listed in the genesis block take turns, each limited to one block in any N/2+1 in a row, and a signer is added or removed by a majority vote of the others. DucatusX, TTcoin Network, Graphlinq Chain, NexDAX Chain, Rubidium, Japan Open Chain, Loop Network
Aura	Authority Round, from OpenEthereum and Substrate. Time is cut into fixed slots, each slot belongs to the next authority on the list, and the list can live in a validator contract. Shyft Network
IBFT 2.0 and QBFT	One authority proposes a block, the others vote on it in three phases, and the block exists only once two thirds commit. Authorities are added or removed by vote. Ozone Chain, Electroneum, BlackFort Exchange Network, Blockchain Foundation for Innovation & Collaboration, Bitcicoin, AME Chain, Marvellex Classic
VeChain PoA 2.0	Authority masternodes, identity-checked and each holding 25 million VET, produce blocks in turn; a committee drawn by verifiable randomness endorses each block. VeChain
Biometric identity	Each validator must prove, by a face scan the network checks against every other validator's, that it is one living person not already validating; only those who pass make blocks, with Substrate's BABE and GRANDPA. One person is one authority, however much stake they hold. Humanode
Subtensor	Bittensor's Substrate chain: Aura block production with GRANDPA finality, among validators the Opentensor Foundation runs. Bittensor
CometBFT with admitted validators	The Cosmos consensus engine, with the validator set fixed by the operator instead of chosen by stake. Mezo
Hyperledger Fabric	An enterprise ledger: members hold certificates from the network's own certificate authority, and an ordering service run by admitted members puts transactions in order. Paycoin
XRP Ledger fork	A copy of rippled whose validators are all run by one company. Cryptonex

Engine not yet documented: AMO Coin.

Methodology — the rules under which each chain's family was decided. Wrapped, staked and pegged claims are listed separately and never counted toward this total.