The Matic Network is a sidechain based scaling solution for public blockchains. Matic aims to allow developers to better scale their Ethereum DApps by using a version of Plasma, along with side chains that use a PoS consensus mechanism. Matic plans on supporting other blockchains as well in order to facilitate interoperability.

Ignis is a blockchain platform that is being developed by Jeluirda; the company behind Ardor and Nxt. Ignis is a child chain of the Nxt blockchain. Jelurida is developing blockchain platforms that will enable users to develop decentralized applications, and will be based on a parent and child chain architecture.
Ignis allows users to create child chains with specific features and to create tokens that meet their needs. This project is closely related to Ardor and Nxt.

Aeternity is a smart contract driven blockchain platform that aims to integrate real world data and improve the overall performance of smart contracts. Aeternity has a hybrid consensus algorithm that combines PoW for verifying transactions, and PoS for governance purposes. The platform is based on a system of state channels that allow users to interact privately with each other and record this information off-chain.