The ZeroMQ core library does not use gsl. We use it in two projects, zproto and zproject, which are nice examples of what is possible without going too meta. I started explaining zproject in my [Scalable C](<a href="http:&#x2F;&#x2F;Scalablec.org" rel="nofollow">http:&#x2F;&#x2F;Scalablec.org</a>) book.