Distributed systems aren’t always traditionally distributed systems. Essentially, any non distributed system that has human involvement in it becomes a distributed system.
Some things that can be modeled as distributed systems that might be unusual:
- Teams, even local ones. CAP Theorem for Software Engineering
- Build Systems, IDEs, Compilers. (Differences Between Build Systems, Package Managers, Compilers, and IDEs)
- Harvest, Yield, and Scalable Tolerant Systems