Apache Airflow — a scheduler for task graphs
Airflow calls itself "an open-source platform for developing, scheduling, and monitoring workflows", batch-oriented data pipelines and ML training included. A DAG carries the schedule, the tasks, their dependencies and callbacks; workflows are "defined entirely in Python"; backfills and re-running failed tasks are built in. Running it means a scheduler, a DAG processor, an API server, a metadata database and, usually, workers.