Another recent scalability proposal is Plasma, which has been proposed by Joseph Poon and Vitalik Buterin. This proposal describes the idea of running smart contracts on root blockchain (Ethereum MainNet) and have child blockchains that perform high number of transactions to feedback small amounts of commitments to the parent chain. In this scheme, blockchains are arranged in a tree hierarchy with mining performed only on the root (main) blockchain which feeds the proofs of security down to child chains. This is also called a Layer-2 system, like state channels also operate on Layer 2, and not on the main chain.
The research paper is available at http://plasma.io.
