Comment by atombender

The documentation site might be a little better: https://docs.nats.io/

NATS is mainly two things:

1. Core NATS, an ephemeral message broker. It's a lightweight pub/sub system where routing of messages is based on wildcard paths. All in memory, lightning fast, extremely lightweight. You can use it for RPC, queues, broadcasting, file transfer, anything.

2. JetStream, which is a Kafka/Pulsar-like log built on top of Core NATS. Streams are indexed, meaning there's no strong need for partitioning or consumer groups, since readers can efficiently filter the stream by interest (you can still partition for write performance). Supports both durable and ephemeral consumers, in-memory streams, ack/nack, priority groups, deduplication, exactly-once delivery, hierarchical clusters, offline clusters ("leaf clusters"), mirroring, etc.

I often find it difficult to explain the magic of NATS. It's a communication model that doesn't really exist anywhere else, as far as I've seen. The closest might be ZeroMQ.

JetStream could be explained as "Kafka for people who don't want to administer Kafka". It's very low-maintenance, very easy to use, feels super lightweight, and still offers much of the performance and reliability of Kafka, as well as a much richer feature set that maps better to what people may want from a streaming log.