Hop

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 Bonders) 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 on the destination chain.

The end result allows users to seamlessly transfer tokens from one network to the next.
The hTokens exist to allow the protocol to mint & burn tokens programatically to move them across chains more easily but also to shorten the native exit time of each scaling solution and allow Bonders to be more capital efficient. Bonders unlock their fronted capital every 24hrs.