Uniswap

Uniswap is the dominant DEX on Ethereum and the protocol that made AMMs mainstream — it's the reference implementation everyone else forked or iterated on. The lineage is worth knowing: v2 (2020) shipped the classic x*y=k pools anyone could deploy permissionlessly; v3 (2021) added concentrated liquidity, where LPs choose a price range instead of providing across all prices, dramatically improving capital efficiency; v4 (2024) introduced hooks — custom logic that runs before/after swaps, letting people build things like limit orders, dynamic fees, or MEV protection on top of the core AMM. The UNI governance token controls the fee switch (currently off) and treasury, and the protocol routinely does $1-2B/day in volume across L1 and L2s.