ZeroMQ wants to be a neutral wrapper in any language but in the end its a C++ library enforcing C++ concepts. You can't map in a straightforward way process concepts from C++ to other languages (also the OS and VM sits in between that). In the end its just mapping programming logic to state machines. There are much better ways to do this and end up with something much more powerful (with first class meta-programming).

I've found ZeroMQ to be an immensely useful and powerful library for certain kinds of distributed queueing applications. It's just a library, not an entire application or web framework to drop practically pre-dictated code into.

Also what "c++ concepts" does it enforce and how? And why is that a bad thing?

ZeroMQ has native stacks in Java, C#, Erlang, C. Also C++.