Please do not associate your comment with "just getting old". This sort of comment unnecessarily perpetuates negative stereotypes in the industry.

And to answer your question, crossbar is an implementation of WAMP (Web Application Messaging Protocol) that is built on top of web sockets. If you are familiar with 1990s technology, think TIBCO for the web.

We used it at a startup in the mid 2010s, and it was great for real time communication between clients (browsers) and servers. Never had any issues.

So at high level its Pub/Sub and RPC combined together in a single framework.

From a developer perspective, you can create a "channel" and then start transmitting messages on that channel. Then someone else can subscribe and can listen to that channel.

In the same way, someone can "expose" a single method. And you as a developer can call that method from anywhere.

The medium of communication is WebSockets. The protocols it uses is WAMP.

Which means any programming language can implement this (on top of WebSockets) and can take advantage of "distributed application architecture".

That's what I'm getting from it, message broker. It says pub/sub and 'routed RPC', wherein a client can register a method and another client can call it...but that's achievable with pub/sub anyway so not really sure what the benefit is.