Optimism (OP)

Transactions execute off the main chain and only the result is posted to Ethereum — that is how an optimistic rollup works, with disputed state challenged by a fraud proof. Optimism's code, known as the OP Stack, became the basis for a whole family of chains joined into the Superchain. Governance is split into two houses: one votes with tokens, the other with participant reputation. The project is also known for handing out funding retroactively to those who already helped the ecosystem.

Withdrawing from an optimistic rollup goes through a challenge period of about a week — the price of not using zero-knowledge proofs.