NATS is a simpler PUB/SUB system that delivers in the UNIX spirit of small composable parts. Apache Pulsar or Apache Kafka deliver the banana, the ape holding it and the rest of the jungle.
It's getting very close. I had wanted to make a production-ready 1.0 release before the end of the year, but we're in the process of switching from protobuf to flatbuffers. Once that is complete, a stable release will be made.