RabbitMQ

RabbitMQ is the message broker that just works. For 15+ years, it's been the default choice for task queues, async processing, and service-to-service communication. Complex routing, priority queues, dead-letter exchanges, and acknowledgment patterns — RabbitMQ handles the messaging patterns that Kafka was never designed for.

If you're building traditional request-response systems, worker queues, or need flexible message routing, RabbitMQ is battle-tested and boring in the best way. Kafka is for event streaming and log aggregation at massive scale — different tool, different job. NATS is the ultra-lightweight option for simple pub-sub. Redis Streams works for in-memory messaging when durability isn't critical.

The catch: RabbitMQ is written in Erlang, which makes operational debugging an adventure. Clustering and high availability are more complex than the docs suggest — mirrored queues were replaced by quorum queues for good reason. And RabbitMQ's throughput caps around 10-100K messages per second, which is fine for most apps but doesn't compete with Kafka at scale.