Hashgraph, on the other hand, is a consensus method that offers a different approach to distributed ledger technology. The white paper defines itself as a data structure or a consensus algorithm and not a complete system, and specifically a distributed ledger technology.

it is patented by Swirlds, and no one other than a license can use it. However, we also have Hedera Hashgraph, and it is a public Hashgraph network. It has all the Hashgraph consensus algorithm features with slight changes in how it utilizes the leader format. It uses gossip about gossip and Virtual Voting as the two techniques to maintain connectivity and consensus.

Website https://en.wikipedia.org/wiki/Hashgraph