Balancer

Balancer is an AMM that generalises constant-product to arbitrary weights and up to 8 tokens per pool. A standard Uniswap pool is fixed 50/50; a Balancer pool can be 80/20 ETH/USDC, or a 25/25/25/25 index of four tokens, and the AMM automatically keeps those weights by rebalancing as trades come in. The mental model: a Balancer pool is a self-rebalancing index fund that also pays you trading fees. Use cases: reducing impermanent loss with asymmetric weights (80/20 pools leak less value on price moves than 50/50), building on-chain index products, and stable pools for correlated assets similar to Curve. Less liquid than Uniswap or Curve, but the architecture is flexible enough that it's become infrastructure for launch pools and custom DeFi primitives.