zkSync (built by Matter Labs)
zkSync (built by Matter Labs) is a scaling and privacy engine for Ethereum. Its current functionality scope includes low gas transfers of ETH and ERC20 tokens in the Ethereum network.
zkSync 1.0 (the current version) will support NFTs and limited orders this spring. zkSync 2.0 (testnet in May, mainnet in August) will bring full EVM support.
PoS, under development
600 gas (the users will be able to go with ~$0.01 when zkPorter is released)
ETH, ERC20 tokens. NFTs soon.