We have devoted the entire book to blockchain-based smart contract development. But there is another ecosystem of cryptocurrencies that are not based on blockchains. These are based on direct acyclic graphs or DAGs. Such systems are called graph-based, distributed ledger technology. Some noteworthy DAG-based DLTs are DagCoin, Byteball, Hashgraph, and Tangle.
DagCoin was the first DAG-based DLT launched in 2012 by Sergio Demian Lerner, pioneer of blockchain-free cryptocurrencies. That was closely followed by Byteball by Anton Churyumov. Hashgraph is currently a private DLT based on DAG, invented by Leemon Baird. Tangle technology was introduced as a whitepaper by Sergey Popov on April 3, 2016. The cryptocurrency on Tangle aims at supporting transactions between Internet-of-Things (IoT) appliances, hence aptly named Iota.
In the following sections, we will...
