Two-phase commit made one transaction span multiple machines by separating preparation from the final decision, but its blocking behavior exposed the cost of making distributed work appear atomic.
Viewstamped Replication independently developed a primary-backup protocol with quorums and view changes, providing an early path to replicated state machines alongside the better-known Paxos lineage.
ZooKeeper turned leader election, membership, configuration and synchronization into reusable patterns built on a small replicated namespace with ordering guarantees, sessions and watches.
Diego Ongaro and John Ousterhout designed Raft around understandability as an explicit engineering goal, separating leader election, replicated logs, safety, and membership changes into a structure intended to be easier to teach and implement than the Paxos literature.
Leslie Lamport's Paxos algorithm gave crash-fault-tolerant distributed systems a rigorous way to agree on values despite delays and failures, but its unusual original presentation also created a second history: decades of work translating the proof into systems engineers could confidently implement.