Morpho uses off-chain order book + on-chain settlement:

User signed interest rate orders (EIP-712)
Matching bot listens to find counterparty
On-chain call matchOrders(), Gas covered by the bot
Result: User zero Gas, matching speed < 5 seconds.
Open-source matching engine, community can build their own bots.
Technical highlights: Off-chain version of the order book. @Morpho Labs 🦋 #Morpho $MORPHO