A look at what's building on JPMorgan's Quorum

Quorum is a permissioned variant of the go-Ethereum client (geth) developed through JPMorgan’s partnership with the Ethereum Enterprise Alliance focusing on financial service applications.

Quorum uses a "QuorumChain" to achieve consensus, based on majority voting of nodes that are permissioned to read and write. Other nodes in system are purely read-only. According to its Github, the permissioned blockchain utilizes Istanbul BFT and Raft-based models to strengthen its fault tolerance.