Ethereum is the leading smart contract platform. It allows developers to build decentralised applications (dApps) and enabled the explosion of DeFi, NFTs, and token issuance. Transitioned from Proof of Work to Proof of Stake in 2022.
Cardano is a proof-of-stake blockchain platform built on peer-reviewed academic research. Founded by Ethereum co-founder Charles Hoskinson, it takes a methodical, research-first approach to development. Its Ouroboros consensus mechanism was the first provably secure PoS protocol.
Polkadot is a Layer 0 multi-chain network that allows different blockchains to interoperate. Created by Ethereum co-founder Gavin Wood, it uses a relay chain and parachain architecture letting multiple specialised blockchains run in parallel and communicate securely.
Avalanche is a smart contract platform that achieves high throughput through a novel Avalanche consensus mechanism. It supports custom blockchains called Subnets, making it attractive for enterprise and gaming. Its C-Chain is EVM-compatible, allowing Ethereum dApps to deploy easily.