The Polkadot blockchain is a multi-chain blockchain that is designed to bundle multiple chains together so that they can be executed in parallel. The goal is for every block on the Polkadot blockchain to contain multiple blocks from other chains. This will enable the network to contain the transaction information from multiple chains and dramatically increase the overall interoperability between different blockchain networks. Polkadot was created by the Web3 Foundation, which is led by Gavin Wood, one of the founders of Ethereum. Polkadot is their flagship project, and aims to solve the issues in the blockchain ecosystem related to disjointed governance and interoperability.
The Nervos Network is an open-source public blockchain ecosystem that is designed to secure multiple assets. Unlike other smart contract platforms that require users to pay transaction fees to help secure the underlying networks, the Nervos Network hopes to create an incentive system that will enable multiple assets to be secured regardless of their price volatility. It does this by capturing the total network value through its native coin the Nervos CKByte, which entitles holders to storage rights on the Nervos blockchain. The network uses a PoW consensus mechanism.