The thesis delivers analyses of multiple types of blockchain systems. We narrow our analysis scope down to consensus algorithms. Specifically, we identify four mainstream types of protocols, from the old-fashioned to the most popular ones: Byzantine fault-tolerant consensus, Nakamoto consensus, (natural) DAG-based protocols, and parallel-chain based protocols. In each type, we analyse one of the top-ranked projects. Our instances include the dBFT protocol in NEO, the proof of authority in Ethereum (Geth), the Tangle network in IOTA, and the weak consensus in Sphinx. Our discussion covers their major properties of security, scalability, and decentralization.