Apache Kafka

https://kafka.apache.org

An event streaming and processing system written in Java. It can be thought of as a distributed append-only log. For a simple message broker, Kafka is overkill.

Features:

Permanent storage
Strict message order
Easy horizontal scalability
Kafka Streams: message filters, joins, aggregations, etc
Kafka Connect: connectors to external systems such as PostgreSQL for data import/export

Learn

https://kafka.apache.org/intro

Concepts:

Event: a recorded fact that something has happened
Topic: an ordered collection of events
Producer: a client that publishes events
Consumer: a client that subscribes to events