AWS Step Functions
Serverless workflow orchestrator — define state machines in JSON/YAML; AWS runs them with built-in retry, parallel, choice, wait, error handling.
Launched 2016. Two modes: Standard (audit-logged, billions of steps possible, 25k tasks/s) and Express (fast, cheap, high-volume, shorter retention). Direct integration with 220+ AWS services without Lambda glue.
Sweet spot: distributed transactions, ETL jobs, ML pipelines, payment workflows. Competitors: Temporal (durable execution, code-first), Argo Workflows (K8s), Cadence, AWS SWF (deprecated predecessor).