Not all the flavors of blockchain rely on costly proof of work consensus mechanism. Bitcoin blockchain uses proof of work where in order to change a record on a blockchain, a complex computational task (proof of work) requiring computing power need to be resolved.
However in Linux Foundation Hyperledger fabric v1.0 does not have the proof of work consensus mechanism as opposed to bitcoin version of the blockchain. Instead it has Practical Byzantine Fault Tolerance (PBFT) consensus mechanism. Consensus that a transaction is valid reached once a certain number identical responses is reached and works best for permissioned blockchains. Here the consensus is already distributed. It also addresses double spending issue. I would like to know how hashgraph is different than fabric.