I've used ZeroMQ lightly as a socket-replacement and for simple IPC and I'd say the key thing it solved was connection establishment. It turns out that opening a two way connection between two apps on the same network without a clear starting order can go wrong in many ways and become quite messy to get right. With ZeroMQ it more or less just magically worked and it allowed me to focus on the actual problem I was working on.

The wide range of language support was also nice. It allowed me to test the interface using a Python notebook which came in handy for debugging.

If you have ever written non trivial TCP sockets code you would notice for many purposes that using this saves you lots of very non trivial socket handling intricacies.

For me 0mq works internally, and not for interfacing outside a closed system. I think that might be the source of some confusion

ZMQ is not a replacement for sockets, it's a library that uses sockets (and other transport mechanisms) underneath. For more details: https://zguide.zeromq.org/docs/preface/#ZeroMQ-in-a-Hundred-...

It's in no way a competing standard.