Messaging and streaming covers the asynchronous-communication layer that sits between services. Apache Kafka is the dominant heavyweight choice for high-throughput event streaming and log-style architectures; RabbitMQ remains common for traditional task queues; NATS and its JetStream extension fill the lightweight-messaging niche; AWS SQS / SNS, Google Pub/Sub, and Azure Service Bus offer the same primitives as managed services.
The patterns repeat across technologies: at-least-once vs exactly-once delivery, idempotent consumers, partitioning strategies, dead-letter queues, ordering guarantees, and the operational model (broker clusters, replication, retention). Most courses pick one technology to teach concretely and assume the patterns transfer to others.