Compound

Compound launched in 2018 and was the first major lending protocol that worked well. It introduced the algorithmic interest rate model that Aave and almost every subsequent protocol adopted. Compound has been quieter than Aave since 2022 but the protocol still works, the team still ships, and the V3 version is technically elegant. Useful to know about as the historical reference point, even if Aave is the more active product today.