First, as complicated as the licensing interactions around the GPL may be, the quite simple fact is that the (L)GPL's requirements only apply if you distribute code, so there is no more reason to take pause when using an LGPLv3 library in backend infrastructure than there would be if you were using a BSD-licensed library.
As for client devices, it is possible to distribute proprietary applications linked with LGPL libraries, though there are requirements you must follow. The amount of time it takes to figure out and comply with those requirements is minimal compared to the person-hours that went into developing ZeroMQ, which you are getting for free.
Edit: apparently ZeroMQ includes a static linking exception to the LGPL, so you don't even have to comply with the LGPL's most onerous restriction when linking with ZeroMQ! http://zeromq.org/area:licensing
Well it's FUD in the sense that I really, actually feel Fear Uncertainty and Doubt about using any code under GPLv3 license. There's good reason to [https://www.google.com/search?q=gplv3+for+commercial+use&oq=... ] worry. Large companies I've worked in before this (with teams of technically savvy lawyers on staff) have been known to promulgate an outright ban of such open source software in their production stack.
Now, nothing makes me happier than being proven wrong in this case (especially with the static linking exception AND this little nugget "It is the intention of the ZeroMQ community to move gradually towards the Mozilla Public License v2, as a replacement for the current LGPLv3 + static link exception" ).
So in a sense, my comment here has had a positive result not just for me but also for anyone else reading this thread and worried about the license. So on balance, I'd credit this subthread more for clearing up of FUD than the reverse ;-)
First, as complicated as the licensing interactions around the GPL may be, the quite simple fact is that the (L)GPL's requirements only apply if you distribute code, so there is no more reason to take pause when using an LGPLv3 library in backend infrastructure than there would be if you were using a BSD-licensed library.
As for client devices, it is possible to distribute proprietary applications linked with LGPL libraries, though there are requirements you must follow. The amount of time it takes to figure out and comply with those requirements is minimal compared to the person-hours that went into developing ZeroMQ, which you are getting for free.
Edit: apparently ZeroMQ includes a static linking exception to the LGPL, so you don't even have to comply with the LGPL's most onerous restriction when linking with ZeroMQ! http://zeromq.org/area:licensing