[malkia]

Not that it matters much, but ZeroMQ is written in C++, while exposing "C" only interface, and then additionally there is a C++ binding to this "C" interface, which IMHO is very robust design (C for API is much easier to access from other langs).

[avalanche123]

You are right, however C bindings in other languages usually look quite ugly and non-idiomatic, but ZeroMQ did great job in that sense and their higher level language bindings are written with language specifics in mind