Azure’s latest service uses WebSockets to deliver a publish-and-subscribe messaging hub.

Node.js has earned its place at the table for good reason. It’s fast, scalable and ideally suited to build everything from real-time chat apps to enterprise-grade systems.

Node.js is an open source cross platform runtime environment for building data-intensive real-time applications that run across distributed devices -- so think server-side network-level applications.

More directly competitive with PubNub are others providing API-based routes to build any kind of data updates, messaging or otherwise, that turn the wheels of any real-time services.