Blockchain technology has been revolutionizing many fields since last decade. Its true potential is not practically utilized yet. In a very short period of time, it has evolved twice - Smart contracts and Directed Acyclic Graph (DAG). DAG based blockchains currently referred to as Blockchain 3.0 solves many issues in the current conventional blockchain technologies including transaction fees, transaction approval times and scalability. In this paper, we present a comparative analysis of blockchain implementations based on DAG including IOTA, NxT, Byteball, Nano, DAGCoin, Fantom, XDAG and Caixapay. We discuss limitations of both conventional and DAG based blockchains and suggest when to prefer DAG based blockchains.

翻译：区块链技术自过去十年来已在众多领域引发革命性变革，其真正潜力尚未得到实际开发。在极短时间内，该技术经历了两次演进——智能合约与有向无环图（DAG）。目前被称为区块链3.0的基于DAG的区块链解决了当前传统区块链技术中的诸多问题，包括交易费用、交易确认时间以及可扩展性。本文对基于DAG的区块链实现（包括IOTA、NxT、Byteball、Nano、DAGCoin、Fantom、XDAG和Caixapay）进行了比较分析。我们讨论了传统区块链与基于DAG的区块链各自的局限性，并提出了优先选择基于DAG的区块链的适用场景。