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.

RChain is building a cross-chain blockchain platform that hopes to improve transaction speeds and scalability. RChain smart contracts are written in Rholang and are run concurrently on the Rho Virtual Machine. Rholang stands for reflective higher-order language, and supports internal concurrent programming to improve smart contract processing.
Rchain supports multiple blockchains on the same node, allowing them to interact and enabling secure cross-chain exchanges of value. It uses a Proof of Stake consensus algorithm and a form of compression called LADL (Logic as a Distributive Law) that is meant to improve DApp performance.
Unlike most blockchains that use public keys to distinguish virtual address spaces, RChain divides its virtual address space into namespaces A namespace is a set of named channels that are used to communicate the location of a network resource. Namespaces allow smart contracts on one blockchain to be visible to system contracts elsewhere on the network. Namespace developers can also use tools and properties to improve system encryption and protocols.
The platform is powered by the RHOC token.

Mixin is a cross-chain payment network for digital assets. Mixin provides a cross-chain solution with built-in smart contracts that facilitates crypto-asset transfers. Developers can also build cross-chain DApps based on Mixin Network protocol.
Mixin also has a messenger that is built on top of their platform and allows users to access their crypto-assets with a phone number and a 6-digit PIN code. Mixin supports Bitcoin, Bitcoin Cash, Litecoin, Ethereum, Ethereum Classic, Ripple, Sia, and plans on adding more.
The network is powered by the XIN token.