Pulsar

Pulsar is what you reach for when Kafka's architecture starts fighting your requirements. It separates compute (brokers) from storage (BookKeeper), so you can scale each independently. Multi-tenancy is built-in, not bolted on. Geo-replication works across data centers. And it handles both streaming and queue patterns natively — no choosing between Kafka and RabbitMQ.

If you're building cloud-native, multi-tenant, or geo-distributed messaging systems, Pulsar's architecture genuinely fits better than Kafka. Kafka is still king for raw throughput — 15x faster writes and a massive ecosystem. RabbitMQ is the battle-tested choice for traditional task queues with complex routing. NATS is the lightweight option for microservices pub-sub.

The catch: Pulsar is complex. You're running brokers plus BookKeeper plus ZooKeeper (being removed) — that's three distributed systems to manage. Kafka's ecosystem is 10x larger: more connectors, more tooling, more engineers who know it. And Pulsar's throughput, while good, doesn't match Kafka's at the high end. For most teams, Kafka's operational simplicity wins.