Flink

Apache Flink, maintained by the Apache Software Foundation, is an open-source distributed processing engine for stateful computations over both real-time (unbounded) and batch (bounded) data streams — used for analytics, event-driven applications, and ETL at scale. It provides exactly-once state consistency, event-time processing, and high-availability deployment with savepoints (so jobs can be paused and resumed without losing state), plus layered APIs — SQL, the DataStream API, and lower-level ProcessFunction — so teams can pick the right level of control for a given job. As foundational streaming infrastructure rather than an end-user tool, it requires real distributed-systems expertise to operate well in production; it's aimed squarely at data engineering teams, not casual users. It's free and open source under the Apache License v2, with active releases (Flink 2.3.0 in June 2026, Flink Agents 0.3.1 in July 2026) showing ongoing development. Good fit for a data engineering team that needs to process high-volume, low-latency event streams reliably at scale.