What are some alternatives?
When comparing NATS and RabbitMQ, you can also consider the following products
Firebase - Firebase is a cloud service designed to power real-time, collaborative applications for mobile and web.
IBM MQ - IBM MQ is messaging middleware that simplifies and accelerates the integration of diverse applications and data across multiple platforms.
Socket.io - Realtime application framework (Node.JS server)
Apache ActiveMQ - Apache ActiveMQ is an open source messaging and integration patterns server.
SignalR - SignalR is a server-side software system designed for writing scalable Internet applications, notably web servers.
Apache Kafka - Apache Kafka is an open-source message broker project developed by the Apache Software Foundation written in Scala.