NATS

NATS is a compact messaging server built for low latency request and reply, publish and subscribe, and streaming workloads. Its distinguishing feature is JetStream, which adds persistence, replay, and deduplicated delivery on top of the core pub/sub, alongside accounts, permissions, clustering, and leaf nodes for linking separate networks.

Teams use it as the internal bus between microservices, for IoT and edge telemetry, and to decouple command execution from request handlers.

Keeping it on infrastructure you own means messages stay in your network, there is no connection or throughput pricing, and JetStream state can be backed up and restored like any other datastore.