Hop is a scalable rollup-to-rollup general token bridge. It allows users to send tokens from one rollup or sidechain to another almost immediately without having to wait for the networks challenge period. It works by involving market makers (referred to as Bonder) who front the liquidity at the destination chain in exchange for a small fee. This credit is extended by the Bonder in form of hTokens which are then swapped for their native token counterpart in an AMM.