Hey there @anooxy - v0.3.2 is the stable build, although that is only for the core code and our bundled plugins, third-party plugin versioning is a little harder to enforce
@scuzz is correct -- master branch contains the latest code, which may or may not be stable (though we try to keep it stable). Right now, it's more or less v0.4.0, minus a couple bugfixes.
I'm currently considering using NodeBB in production and I would love stable branches or tags. I think GitLab actually handles this really well on their github repos!