The blockchain solution provides a trustless, immutable public ledger to record all transactions. Bitcoin is the first public blockchain implementation.. After Bitcoin, many blockchains are implemented, such as Ethereum, Litecoin, EOS, NEO,.. etc. However, blockchain has scalability and performance problems when it is implemented globally. The cost of achieving consensus is very high, either on energy consumption or by sacrificing the security.
DAG, Directed Acyclic Graph, is an alternative solution for a trustless, immutable public ledger without the scalability or the performance problems. Sometimes it is called the next generation of blockchain. There are two algorithms for DAG: HashGraph and Tangle. Tangle is created by IOTA (token IOTA or MIOTA); HashGraph is created by Swirlds, Inc.
Unlike IOTA (Tangle), HashGraph is a patented technology by Swirlds, Inc. Hedera and Constellation are companies developing application platform and issue cryptocurrency by licensing HashGraph technology.
The following diagram shows the relationship between Blockchain and Hashgraph.