*Review* **Distributed Ledger Technology Review and Decentralized Applications Development Guidelines**

**Claudia Antal, Tudor Cioara \*, Ionut Anghel, Marcel Antal and Ioan Salomie**

> Computer Science Department, Technical University of Cluj-Napoca, Memorandumului 28, 400114 Cluj-Napoca, Romania; claudia.pop@cs.utcluj.ro (C.A.); ionut.anghel@cs.utcluj.ro (I.A.); marcel.antal@cs.utcluj.ro (M.A.); ioan.salomie@cs.utcluj.ro (I.S.) **\*** Correspondence: tudor.cioara@cs.utcluj.ro; Tel.: +40-264-202-352

**Abstract:** The Distributed Ledger Technology (DLT) provides an infrastructure for developing decentralized applications with no central authority for registering, sharing, and synchronizing transactions on digital assets. In the last years, it has drawn high interest from the academic community, technology developers, and startups mostly by the advent of its most popular type, blockchain technology. In this paper, we provide a comprehensive overview of DLT analyzing the challenges, provided solutions or alternatives, and their usage for developing decentralized applications. We define a three-tier based architecture for DLT applications to systematically classify the technology solutions described in over 100 papers and startup initiatives. Protocol and Network Tier contains solutions for digital assets registration, transactions, data structure, and privacy and business rules implementation and the creation of peer-to-peer networks, ledger replication, and consensus-based state validation. Scalability and Interoperability Tier solutions address the scalability and interoperability issues with a focus on blockchain technology, where they manifest most often, slowing down its large-scale adoption. The paper closes with a discussion on challenges and opportunities for developing decentralized applications by providing a multi-step guideline for decentralizing the design and implementation of traditional systems.

**Keywords:** distributed ledger technology; blockchain; decentralized applications; technology review; development guidelines; architecture
