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.
NIX is developing a cross-chain protocol with an emphasis on privacy. Their platform will be powered by the NIX coin, and will allow users to exchange supported coins with atomic swaps. Nix hopes to eliminate the need for centralized exchanges with their DEX manager. The platform is based on the Ghost Protocol, which uses elements of Zercoin, and integrates the Tor network to provide enhanced security and privacy for users. NIX allows developers create and attach their own networks to the NIX network as sidechains. The cross-chain platform has a Proof-of-Work consensus mechanism.