Avail is a modular blockchain focussed on data availability: ordering and recording blockchain transactions and making it possible to prove that block data is available without having to download the entire block. This allows for higher scalability than most blockchains.
Avail enables Layer-2 solutions to offer enhanced scalability throughput by leveraging Avail to build Validiums with off-chain data availability. Moreover, by ensuring transaction data availability, Avail allows standalone chains or sidechains with arbitrary execution environments to bootstrap validator security without creating and managing their own validator set.
Avail uses NPoS with a modification in block verification. The stakeholders involved are still validators and nominators.
Light clients can also contribute to data availability on Avail. Avail's consensus requires that two-thirds plus 1 of the validators reach a consensus for validity.