Wallets, keys, validator nodes ran by prime banks.
It's not a blockchain, it's a DAG/Hashgraph.
Currently employed by the following cryptocurrencies:
IOTA
Nano
Obyte
Hedera
Fantom
Pros:
-Thousands of times faster than Eth/Btc
-No mining
-Transaction validation uses VERY little energy
Cons:
-Vulnerable to sybil attacks fed+bank reserves would need be %34 of network to ensure security. ( current reserve rate is %10)
-Traceable.
-Centralized.