Hashgraph
Hashgraph is a blockchain alternative that claims to be faster and more secure by using a different data structure. Nodes relay transaction information, which is called gossip, among each other. When nodes have synchronized information, it's a gossip sync, and they commemorate this with an event, or a transaction record on the hashgraph.
Directed Acyclic Graph
Directed Acyclic Graph (DAG) is another blockchain alternative with its own data structure. Instead of a blockchain, a DAG's structure is more like a graph where transactions are built on top of each other. For a node to initiate a new transaction, it must first validate previous transactions. New transactions with larger numbers of previous transactions underneath them receive priority on the ledger.
Holochain
Holochain is a departure from the typical blockchain structure in that it does away with the global consensus mechanism. Each node is in charge of its own chain and records its own transactions. They're all still part of a network, but they operate independently. Nodes must follow a set of rules, and data validators ensure that nodes comply with these rules. If a node breaks these rules, validators notify the rest of the network.
Advantages to distributed ledger technology
The biggest advantages to distributed ledger technology are security, transparency, and decentralization.
A distributed ledger is much harder to attack than a central database. The network can have nodes around the world, all with their own copies of the ledger, so there's no central point of failure. Distributed ledgers are also immutable and can't be altered by any third party. For example, once a transaction is confirmed on a blockchain, no one can go back and change it later.
All the information on a distributed ledger is available to those on the network. If it's a public ledger, then it's available for anyone in the world to view. In industries where transparency is important, a distributed ledger will typically be a much more suitable choice than a private database.
